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 $146.59   5.264%   $154.3065   $154.31   $154.30   $154.30  
  Purchase #2 $94.89   9.633%   $104.0308   $104.03   $104.05   $104.00  
  Purchase #3 $35.67   10.710%   $39.4903   $39.49   $39.50   $39.50  
  Purchase #4 $184.73   9.674%   $202.6008   $202.60   $202.60   $202.60  
  Purchase #5 $46.28   3.511%   $47.9049   $47.90   $47.90   $47.90  
  Purchase #6 $241.98   13.600%   $274.8893   $274.89   $274.90   $274.90  
  Purchase #7 $210.98   7.622%   $227.0609   $227.06   $227.05   $227.10  
  7 purchase totals = $961.12       $1,050.2835   $1,050.28   $1,050.30   $1,050.30