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 $200.76   7.546%   $215.9093   $215.91   $215.90   $215.90  
  Purchase #2 $183.62   13.306%   $208.0525   $208.05   $208.05   $208.10  
  Purchase #3 $143.49   5.418%   $151.2643   $151.26   $151.25   $151.30  
  Purchase #4 $108.98   12.360%   $122.4499   $122.45   $122.45   $122.40  
  Purchase #5 $33.47   10.774%   $37.0761   $37.08   $37.10   $37.10  
  Purchase #6 $47.73   13.393%   $54.1225   $54.12   $54.10   $54.10  
  Purchase #7 $87.65   7.302%   $94.0502   $94.05   $94.05   $94.10  
  7 purchase totals = $805.70       $882.9248   $882.92   $882.90   $883.00