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 $53.76   4.523%   $56.1916   $56.19   $56.20   $56.20  
  Purchase #2 $20.32   11.247%   $22.6054   $22.61   $22.60   $22.60  
  Purchase #3 $184.34   13.584%   $209.3807   $209.38   $209.40   $209.40  
  Purchase #4 $34.77   6.196%   $36.9243   $36.92   $36.90   $36.90  
  Purchase #5 $42.88   3.543%   $44.3992   $44.40   $44.40   $44.40  
  Purchase #6 $84.78   13.456%   $96.188   $96.19   $96.20   $96.20  
  Purchase #7 $205.80   9.676%   $225.7132   $225.71   $225.70   $225.70  
  7 purchase totals = $626.65       $691.4024   $691.40   $691.40   $691.40