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 $188.46   3.388%   $194.845   $194.85   $194.85   $194.80  
  Purchase #2 $107.77   10.177%   $118.7378   $118.74   $118.75   $118.70  
  Purchase #3 $125.71   10.373%   $138.7499   $138.75   $138.75   $138.70  
  Purchase #4 $93.88   13.712%   $106.7528   $106.75   $106.75   $106.80  
  Purchase #5 $241.63   6.120%   $256.4178   $256.42   $256.40   $256.40  
  Purchase #6 $29.46   10.642%   $32.5951   $32.60   $32.60   $32.60  
  Purchase #7 $67.76   6.644%   $72.262   $72.26   $72.25   $72.30  
  7 purchase totals = $854.67       $920.3604   $920.37   $920.35   $920.30