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 $60.77   9.839%   $66.7492   $66.75   $66.75   $66.70  
  Purchase #2 $172.85   5.306%   $182.0214   $182.02   $182.00   $182.00  
  Purchase #3 $83.77   13.669%   $95.2205   $95.22   $95.20   $95.20  
  Purchase #4 $51.95   3.649%   $53.8457   $53.85   $53.85   $53.80  
  Purchase #5 $168.94   11.122%   $187.7295   $187.73   $187.75   $187.70  
  Purchase #6 $70.34   5.428%   $74.1581   $74.16   $74.15   $74.20  
  Purchase #7 $86.88   5.187%   $91.3865   $91.39   $91.40   $91.40  
  7 purchase totals = $695.50       $751.1109   $751.12   $751.10   $751.00