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 $153.47   6.181%   $162.956   $162.96   $162.95   $163.00  
  Purchase #2 $217.43   9.814%   $238.7686   $238.77   $238.75   $238.80  
  Purchase #3 $40.25   9.426%   $44.044   $44.04   $44.05   $44.00  
  Purchase #4 $160.63   9.409%   $175.7437   $175.74   $175.75   $175.70  
  Purchase #5 $96.38   8.818%   $104.8788   $104.88   $104.90   $104.90  
  Purchase #6 $119.69   5.417%   $126.1736   $126.17   $126.15   $126.20  
  Purchase #7 $153.97   3.680%   $159.6361   $159.64   $159.65   $159.60  
  7 purchase totals = $941.82       $1,012.2008   $1,012.20   $1,012.20   $1,012.20