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 $232.69   13.664%   $264.4848   $264.48   $264.50   $264.50  
  Purchase #2 $98.75   9.410%   $108.0424   $108.04   $108.05   $108.00  
  Purchase #3 $240.92   13.305%   $272.9744   $272.97   $272.95   $273.00  
  Purchase #4 $132.77   13.201%   $150.297   $150.30   $150.30   $150.30  
  Purchase #5 $185.99   11.401%   $207.1947   $207.19   $207.20   $207.20  
  Purchase #6 $123.91   7.844%   $133.6295   $133.63   $133.65   $133.60  
  Purchase #7 $54.37   10.377%   $60.012   $60.01   $60.00   $60.00  
  7 purchase totals = $1,069.40       $1,196.6348   $1,196.62   $1,196.65   $1,196.60