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 $30.88   6.273%   $32.8171   $32.82   $32.80   $32.80  
  Purchase #2 $54.90   10.636%   $60.7392   $60.74   $60.75   $60.70  
  Purchase #3 $100.85   5.456%   $106.3524   $106.35   $106.35   $106.40  
  Purchase #4 $231.64   12.756%   $261.188   $261.19   $261.20   $261.20  
  Purchase #5 $155.40   11.823%   $173.7729   $173.77   $173.75   $173.80  
  Purchase #6 $166.94   9.736%   $183.1933   $183.19   $183.20   $183.20  
  Purchase #7 $110.97   3.388%   $114.7297   $114.73   $114.75   $114.70  
  7 purchase totals = $851.58       $932.7926   $932.79   $932.80   $932.80