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 $216.90   7.425%   $233.0048   $233.00   $233.00   $233.00  
  Purchase #2 $32.78   11.659%   $36.6018   $36.60   $36.60   $36.60  
  Purchase #3 $69.61   11.312%   $77.4843   $77.48   $77.50   $77.50  
  Purchase #4 $88.31   11.254%   $98.2484   $98.25   $98.25   $98.20  
  Purchase #5 $151.64   3.863%   $157.4979   $157.50   $157.50   $157.50  
  Purchase #6 $21.68   10.574%   $23.9724   $23.97   $23.95   $24.00  
  Purchase #7 $180.92   11.313%   $201.3875   $201.39   $201.40   $201.40  
  7 purchase totals = $761.84       $828.1971   $828.19   $828.20   $828.20