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 $208.62   9.137%   $227.6816   $227.68   $227.70   $227.70  
  Purchase #2 $22.92   6.535%   $24.4178   $24.42   $24.40   $24.40  
  Purchase #3 $58.68   9.106%   $64.0234   $64.02   $64.00   $64.00  
  Purchase #4 $227.38   12.263%   $255.2636   $255.26   $255.25   $255.30  
  Purchase #5 $232.57   7.123%   $249.136   $249.14   $249.15   $249.10  
  Purchase #6 $68.26   4.406%   $71.2675   $71.27   $71.25   $71.30  
  Purchase #7 $94.70   10.194%   $104.3537   $104.35   $104.35   $104.40  
  7 purchase totals = $913.13       $996.1436   $996.14   $996.10   $996.20