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 $237.37   6.797%   $253.504   $253.50   $253.50   $253.50  
  Purchase #2 $39.63   8.662%   $43.0628   $43.06   $43.05   $43.10  
  Purchase #3 $221.42   11.667%   $247.2531   $247.25   $247.25   $247.30  
  Purchase #4 $180.59   4.295%   $188.3463   $188.35   $188.35   $188.30  
  Purchase #5 $23.83   12.560%   $26.823   $26.82   $26.80   $26.80  
  Purchase #6 $145.55   11.855%   $162.805   $162.81   $162.80   $162.80  
  Purchase #7 $213.55   5.140%   $224.5265   $224.53   $224.55   $224.50  
  7 purchase totals = $1,061.94       $1,146.3207   $1,146.32   $1,146.30   $1,146.30