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 $51.60   7.334%   $55.3843   $55.38   $55.40   $55.40  
  Purchase #2 $87.86   7.454%   $94.4091   $94.41   $94.40   $94.40  
  Purchase #3 $24.66   8.818%   $26.8345   $26.83   $26.85   $26.80  
  Purchase #4 $47.48   5.272%   $49.9831   $49.98   $50.00   $50.00  
  Purchase #5 $149.54   5.814%   $158.2343   $158.23   $158.25   $158.20  
  Purchase #6 $146.58   13.373%   $166.1821   $166.18   $166.20   $166.20  
  Purchase #7 $77.39   11.605%   $86.3711   $86.37   $86.35   $86.40  
  7 purchase totals = $585.11       $637.3985   $637.38   $637.45   $637.40