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 $119.29   13.329%   $135.1902   $135.19   $135.20   $135.20  
  Purchase #2 $151.96   4.579%   $158.9182   $158.92   $158.90   $158.90  
  Purchase #3 $77.92   12.649%   $87.7761   $87.78   $87.80   $87.80  
  Purchase #4 $72.39   11.354%   $80.6092   $80.61   $80.60   $80.60  
  Purchase #5 $117.26   8.159%   $126.8272   $126.83   $126.85   $126.80  
  Purchase #6 $158.34   3.407%   $163.7346   $163.73   $163.75   $163.70  
  Purchase #7 $236.67   4.816%   $248.068   $248.07   $248.05   $248.10  
  7 purchase totals = $933.83       $1,001.1235   $1,001.13   $1,001.15   $1,001.10