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 $30.36   4.256%   $31.6521   $31.65   $31.65   $31.70  
  Purchase #2 $123.59   12.856%   $139.4787   $139.48   $139.50   $139.50  
  Purchase #3 $173.31   4.578%   $181.2441   $181.24   $181.25   $181.20  
  Purchase #4 $68.76   10.837%   $76.2115   $76.21   $76.20   $76.20  
  Purchase #5 $93.59   8.205%   $101.2691   $101.27   $101.25   $101.30  
  Purchase #6 $144.30   3.335%   $149.1124   $149.11   $149.10   $149.10  
  Purchase #7 $191.67   7.199%   $205.4683   $205.47   $205.45   $205.50  
  7 purchase totals = $825.58       $884.4362   $884.43   $884.40   $884.50