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 $55.71   11.561%   $62.1506   $62.15   $62.15   $62.20  
  Purchase #2 $57.81   6.171%   $61.3775   $61.38   $61.40   $61.40  
  Purchase #3 $20.76   13.108%   $23.4812   $23.48   $23.50   $23.50  
  Purchase #4 $111.30   6.152%   $118.1472   $118.15   $118.15   $118.10  
  Purchase #5 $201.85   5.843%   $213.6441   $213.64   $213.65   $213.60  
  Purchase #6 $210.87   12.140%   $236.4696   $236.47   $236.45   $236.50  
  Purchase #7 $162.63   3.220%   $167.8667   $167.87   $167.85   $167.90  
  7 purchase totals = $820.93       $883.1369   $883.14   $883.15   $883.20