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 $221.75   8.808%   $241.2817   $241.28   $241.30   $241.30  
  Purchase #2 $201.56   7.739%   $217.1587   $217.16   $217.15   $217.20  
  Purchase #3 $59.89   7.178%   $64.1889   $64.19   $64.20   $64.20  
  Purchase #4 $33.90   8.357%   $36.733   $36.73   $36.75   $36.70  
  Purchase #5 $12.56   11.631%   $14.0209   $14.02   $14.00   $14.00  
  Purchase #6 $23.54   8.115%   $25.4503   $25.45   $25.45   $25.50  
  Purchase #7 $197.44   5.837%   $208.9646   $208.96   $208.95   $209.00  
  7 purchase totals = $750.64       $807.7981   $807.79   $807.80   $807.90