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 $50.62   8.814%   $55.0816   $55.08   $55.10   $55.10  
  Purchase #2 $57.68   8.366%   $62.5055   $62.51   $62.50   $62.50  
  Purchase #3 $154.32   6.195%   $163.8801   $163.88   $163.90   $163.90  
  Purchase #4 $92.68   4.873%   $97.1963   $97.20   $97.20   $97.20  
  Purchase #5 $119.92   6.175%   $127.3251   $127.33   $127.35   $127.30  
  Purchase #6 $187.78   11.594%   $209.5512   $209.55   $209.55   $209.60  
  Purchase #7 $205.36   10.243%   $226.395   $226.40   $226.40   $226.40  
  7 purchase totals = $868.36       $941.9348   $941.95   $942.00   $942.00