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 $185.32   5.498%   $195.5089   $195.51   $195.50   $195.50  
  Purchase #2 $111.99   9.536%   $122.6694   $122.67   $122.65   $122.70  
  Purchase #3 $178.60   5.688%   $188.7588   $188.76   $188.75   $188.80  
  Purchase #4 $124.64   4.801%   $130.624   $130.62   $130.60   $130.60  
  Purchase #5 $43.64   10.261%   $48.1179   $48.12   $48.10   $48.10  
  Purchase #6 $123.73   6.794%   $132.1362   $132.14   $132.15   $132.10  
  Purchase #7 $63.25   12.641%   $71.2454   $71.25   $71.25   $71.20  
  7 purchase totals = $831.17       $889.0606   $889.07   $889.00   $889.00