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 $238.54   10.151%   $262.7542   $262.75   $262.75   $262.80  
  Purchase #2 $31.69   3.863%   $32.9142   $32.91   $32.90   $32.90  
  Purchase #3 $233.48   10.193%   $257.2786   $257.28   $257.30   $257.30  
  Purchase #4 $39.61   3.314%   $40.9227   $40.92   $40.90   $40.90  
  Purchase #5 $163.63   8.861%   $178.1293   $178.13   $178.15   $178.10  
  Purchase #6 $230.86   10.444%   $254.971   $254.97   $254.95   $255.00  
  Purchase #7 $71.80   10.361%   $79.2392   $79.24   $79.25   $79.20  
  7 purchase totals = $1,009.61       $1,106.2092   $1,106.20   $1,106.20   $1,106.20