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 $191.82   7.374%   $205.9648   $205.96   $205.95   $206.00  
  Purchase #2 $92.54   5.638%   $97.7574   $97.76   $97.75   $97.80  
  Purchase #3 $106.36   5.517%   $112.2279   $112.23   $112.25   $112.20  
  Purchase #4 $127.54   8.464%   $138.335   $138.34   $138.35   $138.30  
  Purchase #5 $27.34   10.836%   $30.3026   $30.30   $30.30   $30.30  
  Purchase #6 $132.90   12.712%   $149.7942   $149.79   $149.80   $149.80  
  Purchase #7 $59.26   7.103%   $63.4692   $63.47   $63.45   $63.50  
  7 purchase totals = $737.76       $797.8511   $797.85   $797.85   $797.90