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 $51.81   13.105%   $58.5997   $58.60   $58.60   $58.60  
  Purchase #2 $221.99   4.794%   $232.6322   $232.63   $232.65   $232.60  
  Purchase #3 $160.90   8.659%   $174.8323   $174.83   $174.85   $174.80  
  Purchase #4 $47.97   8.740%   $52.1626   $52.16   $52.15   $52.20  
  Purchase #5 $95.82   3.595%   $99.2647   $99.26   $99.25   $99.30  
  Purchase #6 $68.87   8.458%   $74.695   $74.70   $74.70   $74.70  
  Purchase #7 $86.98   13.504%   $98.7258   $98.73   $98.75   $98.70  
  7 purchase totals = $734.34       $790.9123   $790.91   $790.95   $790.90