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 $68.60   4.568%   $71.7336   $71.73   $71.75   $71.70  
  Purchase #2 $217.46   8.760%   $236.5095   $236.51   $236.50   $236.50  
  Purchase #3 $158.56   8.733%   $172.407   $172.41   $172.40   $172.40  
  Purchase #4 $97.54   13.498%   $110.7059   $110.71   $110.70   $110.70  
  Purchase #5 $148.25   6.436%   $157.7914   $157.79   $157.80   $157.80  
  Purchase #6 $31.34   10.871%   $34.747   $34.75   $34.75   $34.70  
  Purchase #7 $236.36   3.649%   $244.9848   $244.98   $245.00   $245.00  
  7 purchase totals = $958.11       $1,028.8792   $1,028.88   $1,028.90   $1,028.80