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 $57.43   12.601%   $64.6668   $64.67   $64.65   $64.70  
  Purchase #2 $190.41   8.185%   $205.9951   $206.00   $206.00   $206.00  
  Purchase #3 $128.80   10.229%   $141.975   $141.98   $142.00   $142.00  
  Purchase #4 $70.43   4.647%   $73.7029   $73.70   $73.70   $73.70  
  Purchase #5 $61.38   5.803%   $64.9419   $64.94   $64.95   $64.90  
  Purchase #6 $71.84   9.461%   $78.6368   $78.64   $78.65   $78.60  
  Purchase #7 $22.38   9.509%   $24.5081   $24.51   $24.50   $24.50  
  7 purchase totals = $602.67       $654.4266   $654.44   $654.45   $654.40