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 $216.42   13.684%   $246.0349   $246.03   $246.05   $246.00  
  Purchase #2 $93.65   11.240%   $104.1763   $104.18   $104.20   $104.20  
  Purchase #3 $85.76   7.664%   $92.3326   $92.33   $92.35   $92.30  
  Purchase #4 $200.88   6.187%   $213.3084   $213.31   $213.30   $213.30  
  Purchase #5 $141.66   4.594%   $148.1679   $148.17   $148.15   $148.20  
  Purchase #6 $21.53   12.643%   $24.252   $24.25   $24.25   $24.30  
  Purchase #7 $109.37   11.803%   $122.2789   $122.28   $122.30   $122.30  
  7 purchase totals = $869.27       $950.5510   $950.55   $950.60   $950.60