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 $151.65   6.792%   $161.9501   $161.95   $161.95   $162.00  
  Purchase #2 $239.96   5.347%   $252.7907   $252.79   $252.80   $252.80  
  Purchase #3 $11.36   13.484%   $12.8918   $12.89   $12.90   $12.90  
  Purchase #4 $53.88   10.848%   $59.7249   $59.72   $59.70   $59.70  
  Purchase #5 $125.76   5.251%   $132.3637   $132.36   $132.35   $132.40  
  Purchase #6 $170.54   12.189%   $191.3271   $191.33   $191.35   $191.30  
  Purchase #7 $132.91   13.784%   $151.2303   $151.23   $151.25   $151.20  
  7 purchase totals = $886.06       $962.2786   $962.27   $962.30   $962.30