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 $205.98   13.443%   $233.6699   $233.67   $233.65   $233.70  
  Purchase #2 $142.94   8.421%   $154.977   $154.98   $155.00   $155.00  
  Purchase #3 $29.73   6.832%   $31.7612   $31.76   $31.75   $31.80  
  Purchase #4 $237.49   6.505%   $252.9387   $252.94   $252.95   $252.90  
  Purchase #5 $69.95   3.335%   $72.2828   $72.28   $72.30   $72.30  
  Purchase #6 $247.66   4.472%   $258.7354   $258.74   $258.75   $258.70  
  Purchase #7 $219.70   13.340%   $249.008   $249.01   $249.00   $249.00  
  7 purchase totals = $1,153.45       $1,253.3730   $1,253.38   $1,253.40   $1,253.40