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 $64.68   7.653%   $69.63   $69.63   $69.65   $69.60  
  Purchase #2 $245.43   3.166%   $253.2003   $253.20   $253.20   $253.20  
  Purchase #3 $149.38   8.121%   $161.5111   $161.51   $161.50   $161.50  
  Purchase #4 $164.30   8.846%   $178.834   $178.83   $178.85   $178.80  
  Purchase #5 $115.85   7.136%   $124.1171   $124.12   $124.10   $124.10  
  Purchase #6 $76.86   10.461%   $84.9003   $84.90   $84.90   $84.90  
  Purchase #7 $122.80   8.607%   $133.3694   $133.37   $133.35   $133.40  
  7 purchase totals = $939.30       $1,005.5622   $1,005.56   $1,005.55   $1,005.50