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 $57.33   6.709%   $61.1763   $61.18   $61.20   $61.20  
  Purchase #2 $69.74   10.102%   $76.7851   $76.79   $76.80   $76.80  
  Purchase #3 $129.48   3.292%   $133.7425   $133.74   $133.75   $133.70  
  Purchase #4 $240.39   4.708%   $251.7076   $251.71   $251.70   $251.70  
  Purchase #5 $117.58   7.585%   $126.4984   $126.50   $126.50   $126.50  
  Purchase #6 $125.33   10.728%   $138.7754   $138.78   $138.80   $138.80  
  Purchase #7 $137.38   10.493%   $151.7953   $151.80   $151.80   $151.80  
  7 purchase totals = $877.23       $940.4806   $940.50   $940.55   $940.50