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 $141.57   11.752%   $158.2073   $158.21   $158.20   $158.20  
  Purchase #2 $190.35   12.761%   $214.6406   $214.64   $214.65   $214.60  
  Purchase #3 $90.65   5.546%   $95.6774   $95.68   $95.70   $95.70  
  Purchase #4 $224.70   12.448%   $252.6707   $252.67   $252.65   $252.70  
  Purchase #5 $226.70   11.530%   $252.8385   $252.84   $252.85   $252.80  
  Purchase #6 $171.98   13.676%   $195.5   $195.50   $195.50   $195.50  
  Purchase #7 $243.48   8.361%   $263.8374   $263.84   $263.85   $263.80  
  7 purchase totals = $1,289.43       $1,433.3719   $1,433.38   $1,433.40   $1,433.30