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 $14.74   10.440%   $16.2789   $16.28   $16.30   $16.30  
  Purchase #2 $161.34   4.367%   $168.3857   $168.39   $168.40   $168.40  
  Purchase #3 $96.57   4.202%   $100.6279   $100.63   $100.65   $100.60  
  Purchase #4 $26.98   7.696%   $29.0564   $29.06   $29.05   $29.10  
  Purchase #5 $35.93   13.554%   $40.8   $40.80   $40.80   $40.80  
  Purchase #6 $242.43   11.732%   $270.8719   $270.87   $270.85   $270.90  
  Purchase #7 $106.28   9.647%   $116.5328   $116.53   $116.55   $116.50  
  7 purchase totals = $684.27       $742.5536   $742.56   $742.60   $742.60