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 $216.35   9.209%   $236.2737   $236.27   $236.25   $236.30  
  Purchase #2 $154.61   10.403%   $170.6941   $170.69   $170.70   $170.70  
  Purchase #3 $199.58   10.159%   $219.8553   $219.86   $219.85   $219.90  
  Purchase #4 $68.33   5.527%   $72.1066   $72.11   $72.10   $72.10  
  Purchase #5 $136.96   5.420%   $144.3832   $144.38   $144.40   $144.40  
  Purchase #6 $229.83   11.562%   $256.4029   $256.40   $256.40   $256.40  
  Purchase #7 $160.45   4.593%   $167.8195   $167.82   $167.80   $167.80  
  7 purchase totals = $1,166.11       $1,267.5353   $1,267.53   $1,267.50   $1,267.60