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 $133.76   7.188%   $143.3747   $143.37   $143.35   $143.40  
  Purchase #2 $166.60   5.778%   $176.2261   $176.23   $176.25   $176.20  
  Purchase #3 $144.42   5.153%   $151.862   $151.86   $151.85   $151.90  
  Purchase #4 $71.80   12.152%   $80.5251   $80.53   $80.55   $80.50  
  Purchase #5 $16.50   5.326%   $17.3788   $17.38   $17.40   $17.40  
  Purchase #6 $35.79   5.605%   $37.796   $37.80   $37.80   $37.80  
  Purchase #7 $86.77   12.278%   $97.4236   $97.42   $97.40   $97.40  
  7 purchase totals = $655.64       $704.5863   $704.59   $704.60   $704.60