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 $95.60   13.761%   $108.7555   $108.76   $108.75   $108.80  
  Purchase #2 $5.38   6.291%   $5.7185   $5.72   $5.70   $5.70  
  Purchase #3 $43.87   5.759%   $46.3965   $46.40   $46.40   $46.40  
  Purchase #4 $190.73   4.304%   $198.939   $198.94   $198.95   $198.90  
  Purchase #5 $148.62   6.697%   $158.5731   $158.57   $158.55   $158.60  
  Purchase #6 $135.31   5.170%   $142.3055   $142.31   $142.30   $142.30  
  Purchase #7 $123.95   8.555%   $134.5539   $134.55   $134.55   $134.60  
  7 purchase totals = $743.46       $795.2420   $795.25   $795.20   $795.30