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 $248.69   10.664%   $275.2103   $275.21   $275.20   $275.20  
  Purchase #2 $244.65   13.365%   $277.3475   $277.35   $277.35   $277.30  
  Purchase #3 $211.41   3.190%   $218.154   $218.15   $218.15   $218.20  
  Purchase #4 $112.58   11.691%   $125.7417   $125.74   $125.75   $125.70  
  Purchase #5 $48.88   6.268%   $51.9438   $51.94   $51.95   $51.90  
  Purchase #6 $81.96   5.685%   $86.6194   $86.62   $86.60   $86.60  
  Purchase #7 $217.32   7.319%   $233.2257   $233.23   $233.25   $233.20  
  7 purchase totals = $1,165.49       $1,268.2424   $1,268.24   $1,268.25   $1,268.10