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 $244.33   6.492%   $260.1919   $260.19   $260.20   $260.20  
  Purchase #2 $13.65   10.391%   $15.0684   $15.07   $15.05   $15.10  
  Purchase #3 $94.66   3.604%   $98.0715   $98.07   $98.05   $98.10  
  Purchase #4 $247.87   8.427%   $268.758   $268.76   $268.75   $268.80  
  Purchase #5 $93.92   8.269%   $101.6862   $101.69   $101.70   $101.70  
  Purchase #6 $176.51   12.741%   $198.9991   $199.00   $199.00   $199.00  
  Purchase #7 $83.90   8.639%   $91.1481   $91.15   $91.15   $91.10  
  7 purchase totals = $954.84       $1,033.9232   $1,033.93   $1,033.90   $1,034.00