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 $171.77   13.234%   $194.502   $194.50   $194.50   $194.50  
  Purchase #2 $214.38   6.181%   $227.6308   $227.63   $227.65   $227.60  
  Purchase #3 $141.51   11.211%   $157.3747   $157.37   $157.35   $157.40  
  Purchase #4 $143.56   10.384%   $158.4673   $158.47   $158.45   $158.50  
  Purchase #5 $177.65   3.553%   $183.9619   $183.96   $183.95   $184.00  
  Purchase #6 $151.74   12.665%   $170.9579   $170.96   $170.95   $171.00  
  Purchase #7 $65.71   12.495%   $73.9205   $73.92   $73.90   $73.90  
  7 purchase totals = $1,066.32       $1,166.8151   $1,166.81   $1,166.75   $1,166.90