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 $93.73   6.422%   $99.7493   $99.75   $99.75   $99.70  
  Purchase #2 $226.25   6.609%   $241.2029   $241.20   $241.20   $241.20  
  Purchase #3 $117.72   5.333%   $123.998   $124.00   $124.00   $124.00  
  Purchase #4 $186.45   10.134%   $205.3448   $205.34   $205.35   $205.30  
  Purchase #5 $247.60   5.488%   $261.1883   $261.19   $261.20   $261.20  
  Purchase #6 $136.67   13.430%   $155.0248   $155.02   $155.00   $155.00  
  Purchase #7 $114.72   10.200%   $126.4214   $126.42   $126.40   $126.40  
  7 purchase totals = $1,123.14       $1,212.9295   $1,212.92   $1,212.90   $1,212.80