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 $200.61   8.674%   $218.0109   $218.01   $218.00   $218.00  
  Purchase #2 $209.96   13.353%   $237.996   $238.00   $238.00   $238.00  
  Purchase #3 $221.92   8.517%   $240.8209   $240.82   $240.80   $240.80  
  Purchase #4 $250.70   13.772%   $285.2264   $285.23   $285.25   $285.20  
  Purchase #5 $102.77   13.519%   $116.6635   $116.66   $116.65   $116.70  
  Purchase #6 $25.88   3.409%   $26.7622   $26.76   $26.75   $26.80  
  Purchase #7 $116.77   7.743%   $125.8115   $125.81   $125.80   $125.80  
  7 purchase totals = $1,128.61       $1,251.2914   $1,251.29   $1,251.25   $1,251.30