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 $226.64   10.129%   $249.5964   $249.60   $249.60   $249.60  
  Purchase #2 $41.44   12.257%   $46.5193   $46.52   $46.50   $46.50  
  Purchase #3 $25.43   4.212%   $26.5011   $26.50   $26.50   $26.50  
  Purchase #4 $188.59   11.462%   $210.2062   $210.21   $210.20   $210.20  
  Purchase #5 $89.98   5.502%   $94.9307   $94.93   $94.95   $94.90  
  Purchase #6 $113.36   5.210%   $119.2661   $119.27   $119.25   $119.30  
  Purchase #7 $169.56   9.219%   $185.1917   $185.19   $185.20   $185.20  
  7 purchase totals = $855.00       $932.2115   $932.22   $932.20   $932.20