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 $141.98   12.521%   $159.7573   $159.76   $159.75   $159.80  
  Purchase #2 $226.70   4.539%   $236.9899   $236.99   $237.00   $237.00  
  Purchase #3 $51.47   3.506%   $53.2745   $53.27   $53.25   $53.30  
  Purchase #4 $107.84   9.150%   $117.7074   $117.71   $117.70   $117.70  
  Purchase #5 $204.33   3.728%   $211.9474   $211.95   $211.95   $211.90  
  Purchase #6 $132.89   3.754%   $137.8787   $137.88   $137.90   $137.90  
  Purchase #7 $40.90   7.726%   $44.0599   $44.06   $44.05   $44.10  
  7 purchase totals = $906.11       $961.6151   $961.62   $961.60   $961.70