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 $30.36   4.441%   $31.7083   $31.71   $31.70   $31.70  
  Purchase #2 $211.31   13.369%   $239.56   $239.56   $239.55   $239.60  
  Purchase #3 $15.95   11.608%   $17.8015   $17.80   $17.80   $17.80  
  Purchase #4 $169.25   4.493%   $176.8544   $176.85   $176.85   $176.90  
  Purchase #5 $209.75   9.248%   $229.1477   $229.15   $229.15   $229.10  
  Purchase #6 $81.76   5.105%   $85.9338   $85.93   $85.95   $85.90  
  Purchase #7 $150.29   3.186%   $155.0782   $155.08   $155.10   $155.10  
  7 purchase totals = $868.67       $936.0839   $936.08   $936.10   $936.10