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 $65.84   12.784%   $74.257   $74.26   $74.25   $74.30  
  Purchase #2 $140.88   13.864%   $160.4116   $160.41   $160.40   $160.40  
  Purchase #3 $22.88   4.792%   $23.9764   $23.98   $24.00   $24.00  
  Purchase #4 $248.60   6.151%   $263.8914   $263.89   $263.90   $263.90  
  Purchase #5 $189.64   13.249%   $214.7654   $214.77   $214.75   $214.80  
  Purchase #6 $131.78   11.400%   $146.8029   $146.80   $146.80   $146.80  
  Purchase #7 $21.92   4.105%   $22.8198   $22.82   $22.80   $22.80  
  7 purchase totals = $821.54       $906.9245   $906.93   $906.90   $907.00