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 $65.96   11.475%   $73.5289   $73.53   $73.55   $73.50  
  Purchase #2 $87.90   11.147%   $97.6982   $97.70   $97.70   $97.70  
  Purchase #3 $63.48   5.134%   $66.7391   $66.74   $66.75   $66.70  
  Purchase #4 $104.85   12.353%   $117.8021   $117.80   $117.80   $117.80  
  Purchase #5 $97.96   3.423%   $101.3132   $101.31   $101.30   $101.30  
  Purchase #6 $226.93   7.705%   $244.415   $244.42   $244.40   $244.40  
  Purchase #7 $37.83   9.818%   $41.5441   $41.54   $41.55   $41.50  
  7 purchase totals = $684.91       $743.0406   $743.04   $743.05   $742.90