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 $87.27   11.762%   $97.5347   $97.53   $97.55   $97.50  
  Purchase #2 $188.93   6.164%   $200.5756   $200.58   $200.60   $200.60  
  Purchase #3 $163.30   10.671%   $180.7257   $180.73   $180.75   $180.70  
  Purchase #4 $133.52   5.814%   $141.2829   $141.28   $141.30   $141.30  
  Purchase #5 $96.62   13.868%   $110.0193   $110.02   $110.00   $110.00  
  Purchase #6 $85.70   11.243%   $95.3353   $95.34   $95.35   $95.30  
  Purchase #7 $124.39   9.666%   $136.4135   $136.41   $136.40   $136.40  
  7 purchase totals = $879.73       $961.8870   $961.89   $961.95   $961.80