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 $238.72   11.855%   $267.0203   $267.02   $267.00   $267.00  
  Purchase #2 $36.34   12.845%   $41.0079   $41.01   $41.00   $41.00  
  Purchase #3 $244.63   5.865%   $258.9775   $258.98   $259.00   $259.00  
  Purchase #4 $69.94   4.814%   $73.3069   $73.31   $73.30   $73.30  
  Purchase #5 $226.99   13.679%   $258.04   $258.04   $258.05   $258.00  
  Purchase #6 $120.42   9.727%   $132.1333   $132.13   $132.15   $132.10  
  Purchase #7 $245.73   11.521%   $274.0406   $274.04   $274.05   $274.00  
  7 purchase totals = $1,182.77       $1,304.5265   $1,304.53   $1,304.55   $1,304.40