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 $124.78   6.545%   $132.9469   $132.95   $132.95   $132.90  
  Purchase #2 $16.36   13.728%   $18.6059   $18.61   $18.60   $18.60  
  Purchase #3 $104.41   10.421%   $115.2906   $115.29   $115.30   $115.30  
  Purchase #4 $26.67   10.686%   $29.52   $29.52   $29.50   $29.50  
  Purchase #5 $139.84   11.826%   $156.3775   $156.38   $156.40   $156.40  
  Purchase #6 $244.39   10.403%   $269.8139   $269.81   $269.80   $269.80  
  Purchase #7 $218.27   11.458%   $243.2794   $243.28   $243.30   $243.30  
  7 purchase totals = $874.72       $965.8342   $965.84   $965.85   $965.80