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 $205.86   8.594%   $223.5516   $223.55   $223.55   $223.60  
  Purchase #2 $167.80   3.622%   $173.8777   $173.88   $173.90   $173.90  
  Purchase #3 $84.53   9.578%   $92.6263   $92.63   $92.65   $92.60  
  Purchase #4 $180.69   13.528%   $205.1337   $205.13   $205.15   $205.10  
  Purchase #5 $189.43   5.299%   $199.4679   $199.47   $199.45   $199.50  
  Purchase #6 $215.92   13.559%   $245.1966   $245.20   $245.20   $245.20  
  Purchase #7 $95.57   11.322%   $106.3904   $106.39   $106.40   $106.40  
  7 purchase totals = $1,139.80       $1,246.2442   $1,246.25   $1,246.30   $1,246.30