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 $71.63   6.506%   $76.2902   $76.29   $76.30   $76.30  
  Purchase #2 $236.77   10.694%   $262.0902   $262.09   $262.10   $262.10  
  Purchase #3 $47.91   8.603%   $52.0317   $52.03   $52.05   $52.00  
  Purchase #4 $113.46   8.382%   $122.9702   $122.97   $122.95   $123.00  
  Purchase #5 $159.63   3.354%   $164.984   $164.98   $165.00   $165.00  
  Purchase #6 $162.43   9.814%   $178.3709   $178.37   $178.35   $178.40  
  Purchase #7 $123.94   9.144%   $135.2731   $135.27   $135.25   $135.30  
  7 purchase totals = $915.77       $992.0103   $992.00   $992.00   $992.10