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 $214.64   12.308%   $241.0579   $241.06   $241.05   $241.10  
  Purchase #2 $231.49   11.176%   $257.3613   $257.36   $257.35   $257.40  
  Purchase #3 $65.25   12.239%   $73.2359   $73.24   $73.25   $73.20  
  Purchase #4 $128.45   6.197%   $136.41   $136.41   $136.40   $136.40  
  Purchase #5 $90.80   4.445%   $94.8361   $94.84   $94.85   $94.80  
  Purchase #6 $231.61   8.538%   $251.3849   $251.38   $251.40   $251.40  
  Purchase #7 $186.40   6.665%   $198.8236   $198.82   $198.80   $198.80  
  7 purchase totals = $1,148.64       $1,253.1097   $1,253.11   $1,253.10   $1,253.10