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 $210.89   7.312%   $226.3103   $226.31   $226.30   $226.30  
  Purchase #2 $200.83   13.246%   $227.4319   $227.43   $227.45   $227.40  
  Purchase #3 $132.38   8.220%   $143.2616   $143.26   $143.25   $143.30  
  Purchase #4 $22.83   13.339%   $25.8753   $25.88   $25.90   $25.90  
  Purchase #5 $41.50   3.583%   $42.9869   $42.99   $43.00   $43.00  
  Purchase #6 $20.59   10.401%   $22.7316   $22.73   $22.75   $22.70  
  Purchase #7 $208.95   8.284%   $226.2594   $226.26   $226.25   $226.30  
  7 purchase totals = $837.97       $914.8570   $914.86   $914.90   $914.90