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 $194.47   13.775%   $221.2582   $221.26   $221.25   $221.30  
  Purchase #2 $59.63   10.340%   $65.7957   $65.80   $65.80   $65.80  
  Purchase #3 $190.45   6.296%   $202.4407   $202.44   $202.45   $202.40  
  Purchase #4 $70.74   6.502%   $75.3395   $75.34   $75.35   $75.30  
  Purchase #5 $157.75   10.750%   $174.7081   $174.71   $174.70   $174.70  
  Purchase #6 $221.65   5.762%   $234.4215   $234.42   $234.40   $234.40  
  Purchase #7 $53.95   11.728%   $60.2773   $60.28   $60.30   $60.30  
  7 purchase totals = $948.64       $1,034.2410   $1,034.25   $1,034.25   $1,034.20