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 $209.50   6.728%   $223.5952   $223.60   $223.60   $223.60  
  Purchase #2 $62.37   3.270%   $64.4095   $64.41   $64.40   $64.40  
  Purchase #3 $193.73   6.476%   $206.276   $206.28   $206.30   $206.30  
  Purchase #4 $210.80   10.489%   $232.9108   $232.91   $232.90   $232.90  
  Purchase #5 $179.52   3.194%   $185.2539   $185.25   $185.25   $185.30  
  Purchase #6 $132.36   8.714%   $143.8939   $143.89   $143.90   $143.90  
  Purchase #7 $220.87   8.338%   $239.2861   $239.29   $239.30   $239.30  
  7 purchase totals = $1,209.15       $1,295.6254   $1,295.63   $1,295.65   $1,295.70