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 $162.85   3.476%   $168.5107   $168.51   $168.50   $168.50  
  Purchase #2 $71.86   4.130%   $74.8278   $74.83   $74.85   $74.80  
  Purchase #3 $58.65   12.110%   $65.7525   $65.75   $65.75   $65.80  
  Purchase #4 $87.57   11.651%   $97.7728   $97.77   $97.75   $97.80  
  Purchase #5 $244.51   10.643%   $270.5332   $270.53   $270.55   $270.50  
  Purchase #6 $152.62   3.455%   $157.893   $157.89   $157.90   $157.90  
  Purchase #7 $170.98   12.344%   $192.0858   $192.09   $192.10   $192.10  
  7 purchase totals = $949.04       $1,027.3758   $1,027.37   $1,027.40   $1,027.40