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 $36.82   12.123%   $41.2837   $41.28   $41.30   $41.30  
  Purchase #2 $208.46   6.665%   $222.3539   $222.35   $222.35   $222.40  
  Purchase #3 $23.55   10.398%   $25.9987   $26.00   $26.00   $26.00  
  Purchase #4 $193.62   12.167%   $217.1777   $217.18   $217.20   $217.20  
  Purchase #5 $88.81   11.608%   $99.1191   $99.12   $99.10   $99.10  
  Purchase #6 $167.63   13.854%   $190.8535   $190.85   $190.85   $190.90  
  Purchase #7 $26.39   11.462%   $29.4148   $29.41   $29.40   $29.40  
  7 purchase totals = $745.28       $826.2014   $826.19   $826.20   $826.30