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 $104.72   13.606%   $118.9682   $118.97   $118.95   $119.00  
  Purchase #2 $105.92   9.361%   $115.8352   $115.84   $115.85   $115.80  
  Purchase #3 $47.89   5.656%   $50.5987   $50.60   $50.60   $50.60  
  Purchase #4 $5.74   5.115%   $6.0336   $6.03   $6.05   $6.00  
  Purchase #5 $194.99   7.851%   $210.2987   $210.30   $210.30   $210.30  
  Purchase #6 $46.92   3.183%   $48.4135   $48.41   $48.40   $48.40  
  Purchase #7 $65.66   4.209%   $68.4236   $68.42   $68.40   $68.40  
  7 purchase totals = $571.84       $618.5715   $618.57   $618.55   $618.50