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 $205.98   13.256%   $233.2847   $233.28   $233.30   $233.30  
  Purchase #2 $107.36   5.758%   $113.5418   $113.54   $113.55   $113.50  
  Purchase #3 $71.85   13.129%   $81.2832   $81.28   $81.30   $81.30  
  Purchase #4 $11.75   11.506%   $13.102   $13.10   $13.10   $13.10  
  Purchase #5 $176.50   9.428%   $193.1404   $193.14   $193.15   $193.10  
  Purchase #6 $61.84   13.180%   $69.9905   $69.99   $70.00   $70.00  
  Purchase #7 $122.39   3.594%   $126.7887   $126.79   $126.80   $126.80  
  7 purchase totals = $757.67       $831.1313   $831.12   $831.20   $831.10