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 $246.49   5.345%   $259.6649   $259.66   $259.65   $259.70  
  Purchase #2 $50.79   5.512%   $53.5895   $53.59   $53.60   $53.60  
  Purchase #3 $69.72   9.561%   $76.3859   $76.39   $76.40   $76.40  
  Purchase #4 $50.55   5.109%   $53.1326   $53.13   $53.15   $53.10  
  Purchase #5 $212.81   6.357%   $226.3383   $226.34   $226.35   $226.30  
  Purchase #6 $85.89   10.197%   $94.6482   $94.65   $94.65   $94.60  
  Purchase #7 $250.91   8.669%   $272.6614   $272.66   $272.65   $272.70  
  7 purchase totals = $967.16       $1,036.4208   $1,036.42   $1,036.45   $1,036.40