Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.96   9.110%   $267.2759   $267.28   $267.30   $267.30  
  Purchase #2 $147.94   5.647%   $156.2942   $156.29   $156.30   $156.30  
  Purchase #3 $139.37   3.779%   $144.6368   $144.64   $144.65   $144.60  
  Purchase #4 $172.61   8.874%   $187.9274   $187.93   $187.95   $187.90  
  Purchase #5 $180.79   10.235%   $199.2939   $199.29   $199.30   $199.30  
  Purchase #6 $180.39   13.416%   $204.5911   $204.59   $204.60   $204.60  
  Purchase #7 $196.30   13.492%   $222.7848   $222.78   $222.80   $222.80  
  7 purchase totals = $1,262.36       $1,382.8041   $1,382.80   $1,382.90   $1,382.80