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 $124.76   13.534%   $141.645   $141.65   $141.65   $141.60  
  Purchase #2 $69.49   11.224%   $77.2896   $77.29   $77.30   $77.30  
  Purchase #3 $48.45   11.844%   $54.1884   $54.19   $54.20   $54.20  
  Purchase #4 $205.95   5.633%   $217.5512   $217.55   $217.55   $217.60  
  Purchase #5 $112.54   8.171%   $121.7356   $121.74   $121.75   $121.70  
  Purchase #6 $148.97   12.826%   $168.0769   $168.08   $168.10   $168.10  
  Purchase #7 $30.47   5.481%   $32.1401   $32.14   $32.15   $32.10  
  7 purchase totals = $740.63       $812.6268   $812.64   $812.70   $812.60