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 $117.33   7.613%   $126.2623   $126.26   $126.25   $126.30  
  Purchase #2 $40.88   12.615%   $46.037   $46.04   $46.05   $46.00  
  Purchase #3 $48.41   7.607%   $52.0925   $52.09   $52.10   $52.10  
  Purchase #4 $110.26   10.361%   $121.684   $121.68   $121.70   $121.70  
  Purchase #5 $75.73   10.167%   $83.4295   $83.43   $83.45   $83.40  
  Purchase #6 $124.99   12.834%   $141.0312   $141.03   $141.05   $141.00  
  Purchase #7 $245.59   12.274%   $275.7337   $275.73   $275.75   $275.70  
  7 purchase totals = $763.19       $846.2702   $846.26   $846.35   $846.20