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 $232.46   5.386%   $244.9803   $244.98   $245.00   $245.00  
  Purchase #2 $124.44   3.869%   $129.2546   $129.25   $129.25   $129.30  
  Purchase #3 $190.27   4.709%   $199.2298   $199.23   $199.25   $199.20  
  Purchase #4 $152.36   7.677%   $164.0567   $164.06   $164.05   $164.10  
  Purchase #5 $12.33   5.202%   $12.9714   $12.97   $12.95   $13.00  
  Purchase #6 $63.63   11.492%   $70.9424   $70.94   $70.95   $70.90  
  Purchase #7 $113.60   10.375%   $125.386   $125.39   $125.40   $125.40  
  7 purchase totals = $889.09       $946.8212   $946.82   $946.85   $946.90