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 $109.58   8.396%   $118.7803   $118.78   $118.80   $118.80  
  Purchase #2 $96.88   5.748%   $102.4487   $102.45   $102.45   $102.40  
  Purchase #3 $63.78   3.394%   $65.9447   $65.94   $65.95   $65.90  
  Purchase #4 $245.28   5.847%   $259.6215   $259.62   $259.60   $259.60  
  Purchase #5 $173.33   12.749%   $195.4278   $195.43   $195.45   $195.40  
  Purchase #6 $47.69   12.295%   $53.5535   $53.55   $53.55   $53.60  
  Purchase #7 $144.36   11.747%   $161.318   $161.32   $161.30   $161.30  
  7 purchase totals = $880.90       $957.0945   $957.09   $957.10   $957.00