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 $60.29   8.121%   $65.1862   $65.19   $65.20   $65.20  
  Purchase #2 $123.78   10.787%   $137.1321   $137.13   $137.15   $137.10  
  Purchase #3 $31.41   11.126%   $34.9047   $34.90   $34.90   $34.90  
  Purchase #4 $170.64   8.400%   $184.9738   $184.97   $184.95   $185.00  
  Purchase #5 $19.94   12.874%   $22.5071   $22.51   $22.50   $22.50  
  Purchase #6 $225.79   9.567%   $247.3913   $247.39   $247.40   $247.40  
  Purchase #7 $227.45   7.214%   $243.8582   $243.86   $243.85   $243.90  
  7 purchase totals = $859.30       $935.9534   $935.95   $935.95   $936.00