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 $55.80   8.360%   $60.4649   $60.46   $60.45   $60.50  
  Purchase #2 $93.86   13.845%   $106.8549   $106.85   $106.85   $106.90  
  Purchase #3 $103.64   11.198%   $115.2456   $115.25   $115.25   $115.20  
  Purchase #4 $50.47   11.209%   $56.1272   $56.13   $56.15   $56.10  
  Purchase #5 $87.45   8.550%   $94.927   $94.93   $94.95   $94.90  
  Purchase #6 $82.74   4.194%   $86.2101   $86.21   $86.20   $86.20  
  Purchase #7 $205.38   13.828%   $233.7799   $233.78   $233.80   $233.80  
  7 purchase totals = $679.34       $753.6096   $753.61   $753.65   $753.60