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 $248.89   4.723%   $260.6451   $260.65   $260.65   $260.60  
  Purchase #2 $124.79   4.851%   $130.8436   $130.84   $130.85   $130.80  
  Purchase #3 $78.74   9.212%   $85.9935   $85.99   $86.00   $86.00  
  Purchase #4 $101.63   5.234%   $106.9493   $106.95   $106.95   $106.90  
  Purchase #5 $19.72   4.327%   $20.5733   $20.57   $20.55   $20.60  
  Purchase #6 $151.62   10.313%   $167.2566   $167.26   $167.25   $167.30  
  Purchase #7 $82.29   4.225%   $85.7668   $85.77   $85.75   $85.80  
  7 purchase totals = $807.68       $858.0282   $858.03   $858.00   $858.00