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 $58.97   3.178%   $60.8441   $60.84   $60.85   $60.80  
  Purchase #2 $126.44   5.429%   $133.3044   $133.30   $133.30   $133.30  
  Purchase #3 $159.36   5.430%   $168.0132   $168.01   $168.00   $168.00  
  Purchase #4 $92.80   10.301%   $102.3593   $102.36   $102.35   $102.40  
  Purchase #5 $95.27   10.121%   $104.9123   $104.91   $104.90   $104.90  
  Purchase #6 $154.94   4.726%   $162.2625   $162.26   $162.25   $162.30  
  Purchase #7 $205.92   7.194%   $220.7339   $220.73   $220.75   $220.70  
  7 purchase totals = $893.70       $952.4297   $952.41   $952.40   $952.40