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 $69.59   13.703%   $79.1259   $79.13   $79.15   $79.10  
  Purchase #2 $195.47   4.340%   $203.9534   $203.95   $203.95   $204.00  
  Purchase #3 $109.94   3.350%   $113.623   $113.62   $113.60   $113.60  
  Purchase #4 $154.63   7.411%   $166.0896   $166.09   $166.10   $166.10  
  Purchase #5 $190.62   10.485%   $210.6065   $210.61   $210.60   $210.60  
  Purchase #6 $51.65   5.714%   $54.6013   $54.60   $54.60   $54.60  
  Purchase #7 $173.43   13.856%   $197.4605   $197.46   $197.45   $197.50  
  7 purchase totals = $945.33       $1,025.4602   $1,025.46   $1,025.45   $1,025.50