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 $111.57   6.632%   $118.9693   $118.97   $118.95   $119.00  
  Purchase #2 $41.75   10.815%   $46.2653   $46.27   $46.25   $46.30  
  Purchase #3 $125.53   5.643%   $132.6137   $132.61   $132.60   $132.60  
  Purchase #4 $10.53   7.763%   $11.3474   $11.35   $11.35   $11.30  
  Purchase #5 $23.61   5.839%   $24.9886   $24.99   $25.00   $25.00  
  Purchase #6 $150.88   13.286%   $170.9259   $170.93   $170.95   $170.90  
  Purchase #7 $248.80   4.763%   $260.6503   $260.65   $260.65   $260.70  
  7 purchase totals = $712.67       $765.7605   $765.77   $765.75   $765.80