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 $64.59   4.741%   $67.6522   $67.65   $67.65   $67.70  
  Purchase #2 $9.37   10.830%   $10.3848   $10.38   $10.40   $10.40  
  Purchase #3 $136.25   8.105%   $147.2931   $147.29   $147.30   $147.30  
  Purchase #4 $238.61   8.490%   $258.868   $258.87   $258.85   $258.90  
  Purchase #5 $88.42   5.573%   $93.3476   $93.35   $93.35   $93.30  
  Purchase #6 $185.62   11.494%   $206.9552   $206.96   $206.95   $207.00  
  Purchase #7 $47.35   9.428%   $51.8142   $51.81   $51.80   $51.80  
  7 purchase totals = $770.21       $836.3151   $836.31   $836.30   $836.40