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 $244.95   10.677%   $271.1033   $271.10   $271.10   $271.10  
  Purchase #2 $241.26   6.744%   $257.5306   $257.53   $257.55   $257.50  
  Purchase #3 $122.60   13.746%   $139.4526   $139.45   $139.45   $139.50  
  Purchase #4 $81.42   5.558%   $85.9453   $85.95   $85.95   $85.90  
  Purchase #5 $211.71   13.778%   $240.8794   $240.88   $240.90   $240.90  
  Purchase #6 $116.65   13.512%   $132.4117   $132.41   $132.40   $132.40  
  Purchase #7 $176.40   8.783%   $191.8932   $191.89   $191.90   $191.90  
  7 purchase totals = $1,194.99       $1,319.2161   $1,319.21   $1,319.25   $1,319.20