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 $88.67   11.108%   $98.5195   $98.52   $98.50   $98.50  
  Purchase #2 $139.41   5.829%   $147.5362   $147.54   $147.55   $147.50  
  Purchase #3 $114.37   6.575%   $121.8898   $121.89   $121.90   $121.90  
  Purchase #4 $223.67   5.667%   $236.3454   $236.35   $236.35   $236.30  
  Purchase #5 $126.42   8.862%   $137.6233   $137.62   $137.60   $137.60  
  Purchase #6 $238.88   9.574%   $261.7504   $261.75   $261.75   $261.80  
  Purchase #7 $49.71   8.672%   $54.0209   $54.02   $54.00   $54.00  
  7 purchase totals = $981.13       $1,057.6855   $1,057.69   $1,057.65   $1,057.60