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 $56.71   3.303%   $58.5831   $58.58   $58.60   $58.60  
  Purchase #2 $45.93   8.750%   $49.9489   $49.95   $49.95   $49.90  
  Purchase #3 $157.72   7.518%   $169.5774   $169.58   $169.60   $169.60  
  Purchase #4 $182.61   11.671%   $203.9224   $203.92   $203.90   $203.90  
  Purchase #5 $185.34   8.324%   $200.7677   $200.77   $200.75   $200.80  
  Purchase #6 $211.25   6.193%   $224.3327   $224.33   $224.35   $224.30  
  Purchase #7 $136.28   12.804%   $153.7293   $153.73   $153.75   $153.70  
  7 purchase totals = $975.84       $1,060.8615   $1,060.86   $1,060.90   $1,060.80