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 $84.71   13.595%   $96.2263   $96.23   $96.25   $96.20  
  Purchase #2 $91.95   9.749%   $100.9142   $100.91   $100.90   $100.90  
  Purchase #3 $99.76   12.667%   $112.3966   $112.40   $112.40   $112.40  
  Purchase #4 $64.56   13.641%   $73.3666   $73.37   $73.35   $73.40  
  Purchase #5 $86.78   7.568%   $93.3475   $93.35   $93.35   $93.30  
  Purchase #6 $215.83   11.759%   $241.2094   $241.21   $241.20   $241.20  
  Purchase #7 $161.89   10.199%   $178.4012   $178.40   $178.40   $178.40  
  7 purchase totals = $805.48       $895.8618   $895.87   $895.85   $895.80