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 $188.48   7.817%   $203.2135   $203.21   $203.20   $203.20  
  Purchase #2 $60.56   3.378%   $62.6057   $62.61   $62.60   $62.60  
  Purchase #3 $114.32   4.508%   $119.4735   $119.47   $119.45   $119.50  
  Purchase #4 $70.75   7.560%   $76.0987   $76.10   $76.10   $76.10  
  Purchase #5 $19.58   5.848%   $20.725   $20.73   $20.75   $20.70  
  Purchase #6 $205.95   9.754%   $226.0384   $226.04   $226.05   $226.00  
  Purchase #7 $141.39   10.764%   $156.6092   $156.61   $156.60   $156.60  
  7 purchase totals = $801.03       $864.7640   $864.77   $864.75   $864.70