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 $222.94   11.569%   $248.7319   $248.73   $248.75   $248.70  
  Purchase #2 $130.60   11.690%   $145.8671   $145.87   $145.85   $145.90  
  Purchase #3 $118.38   5.809%   $125.2567   $125.26   $125.25   $125.30  
  Purchase #4 $74.86   8.774%   $81.4282   $81.43   $81.45   $81.40  
  Purchase #5 $46.78   9.290%   $51.1259   $51.13   $51.15   $51.10  
  Purchase #6 $206.25   13.680%   $234.465   $234.47   $234.45   $234.50  
  Purchase #7 $104.92   11.500%   $116.9858   $116.99   $117.00   $117.00  
  7 purchase totals = $904.73       $1,003.8606   $1,003.88   $1,003.90   $1,003.90