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 $226.33   3.207%   $233.5884   $233.59   $233.60   $233.60  
  Purchase #2 $8.33   3.559%   $8.6265   $8.63   $8.65   $8.60  
  Purchase #3 $237.65   9.535%   $260.3099   $260.31   $260.30   $260.30  
  Purchase #4 $119.44   5.808%   $126.3771   $126.38   $126.40   $126.40  
  Purchase #5 $190.78   8.172%   $206.3705   $206.37   $206.35   $206.40  
  Purchase #6 $187.54   5.420%   $197.7047   $197.70   $197.70   $197.70  
  Purchase #7 $31.49   11.131%   $34.9952   $35.00   $35.00   $35.00  
  7 purchase totals = $1,001.56       $1,067.9723   $1,067.98   $1,068.00   $1,068.00