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 $62.47   13.502%   $70.9047   $70.90   $70.90   $70.90  
  Purchase #2 $94.48   11.633%   $105.4709   $105.47   $105.45   $105.50  
  Purchase #3 $162.50   3.631%   $168.4004   $168.40   $168.40   $168.40  
  Purchase #4 $203.46   8.682%   $221.1244   $221.12   $221.10   $221.10  
  Purchase #5 $112.56   7.873%   $121.4218   $121.42   $121.40   $121.40  
  Purchase #6 $104.84   3.438%   $108.4444   $108.44   $108.45   $108.40  
  Purchase #7 $34.54   5.147%   $36.3178   $36.32   $36.30   $36.30  
  7 purchase totals = $774.85       $832.0844   $832.07   $832.00   $832.00