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 $143.34   10.327%   $158.1427   $158.14   $158.15   $158.10  
  Purchase #2 $101.72   4.631%   $106.4307   $106.43   $106.45   $106.40  
  Purchase #3 $178.44   8.181%   $193.0382   $193.04   $193.05   $193.00  
  Purchase #4 $225.79   3.308%   $233.2591   $233.26   $233.25   $233.30  
  Purchase #5 $106.69   11.511%   $118.9711   $118.97   $118.95   $119.00  
  Purchase #6 $39.85   13.416%   $45.1963   $45.20   $45.20   $45.20  
  Purchase #7 $99.38   5.488%   $104.834   $104.83   $104.85   $104.80  
  7 purchase totals = $895.21       $959.8721   $959.87   $959.90   $959.80