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 $59.73   12.809%   $67.3808   $67.38   $67.40   $67.40  
  Purchase #2 $194.27   5.636%   $205.2191   $205.22   $205.20   $205.20  
  Purchase #3 $64.63   7.716%   $69.6169   $69.62   $69.60   $69.60  
  Purchase #4 $162.37   12.697%   $182.9861   $182.99   $183.00   $183.00  
  Purchase #5 $184.80   8.597%   $200.6873   $200.69   $200.70   $200.70  
  Purchase #6 $77.62   13.761%   $88.3013   $88.30   $88.30   $88.30  
  Purchase #7 $213.73   3.819%   $221.8923   $221.89   $221.90   $221.90  
  7 purchase totals = $957.15       $1,036.0838   $1,036.09   $1,036.10   $1,036.10