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 $233.69   11.102%   $259.6343   $259.63   $259.65   $259.60  
  Purchase #2 $240.67   10.505%   $265.9524   $265.95   $265.95   $266.00  
  Purchase #3 $127.30   8.379%   $137.9665   $137.97   $137.95   $138.00  
  Purchase #4 $7.34   5.846%   $7.7691   $7.77   $7.75   $7.80  
  Purchase #5 $245.90   7.308%   $263.8704   $263.87   $263.85   $263.90  
  Purchase #6 $77.41   12.231%   $86.878   $86.88   $86.90   $86.90  
  Purchase #7 $205.80   12.133%   $230.7697   $230.77   $230.75   $230.80  
  7 purchase totals = $1,138.11       $1,252.8404   $1,252.84   $1,252.80   $1,253.00