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 $213.94   13.838%   $243.545   $243.55   $243.55   $243.50  
  Purchase #2 $111.83   4.115%   $116.4318   $116.43   $116.45   $116.40  
  Purchase #3 $24.98   3.614%   $25.8828   $25.88   $25.90   $25.90  
  Purchase #4 $97.99   6.214%   $104.0791   $104.08   $104.10   $104.10  
  Purchase #5 $58.49   4.258%   $60.9805   $60.98   $61.00   $61.00  
  Purchase #6 $153.56   10.667%   $169.9402   $169.94   $169.95   $169.90  
  Purchase #7 $124.71   8.300%   $135.0609   $135.06   $135.05   $135.10  
  7 purchase totals = $785.50       $855.9203   $855.92   $856.00   $855.90