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 $53.38   11.738%   $59.6457   $59.65   $59.65   $59.60  
  Purchase #2 $226.44   6.745%   $241.7134   $241.71   $241.70   $241.70  
  Purchase #3 $58.31   12.543%   $65.6238   $65.62   $65.60   $65.60  
  Purchase #4 $128.38   5.244%   $135.1122   $135.11   $135.10   $135.10  
  Purchase #5 $11.99   10.863%   $13.2925   $13.29   $13.30   $13.30  
  Purchase #6 $62.28   5.230%   $65.5372   $65.54   $65.55   $65.50  
  Purchase #7 $28.49   7.448%   $30.6119   $30.61   $30.60   $30.60  
  7 purchase totals = $569.27       $611.5367   $611.53   $611.50   $611.40