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 $85.38   12.162%   $95.7639   $95.76   $95.75   $95.80  
  Purchase #2 $230.69   8.243%   $249.7058   $249.71   $249.70   $249.70  
  Purchase #3 $6.42   5.168%   $6.7518   $6.75   $6.75   $6.80  
  Purchase #4 $200.44   7.327%   $215.1262   $215.13   $215.15   $215.10  
  Purchase #5 $125.85   10.204%   $138.6917   $138.69   $138.70   $138.70  
  Purchase #6 $46.47   3.461%   $48.0783   $48.08   $48.10   $48.10  
  Purchase #7 $44.71   3.666%   $46.3491   $46.35   $46.35   $46.30  
  7 purchase totals = $739.96       $800.4668   $800.47   $800.50   $800.50