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 $55.47   11.282%   $61.7281   $61.73   $61.75   $61.70  
  Purchase #2 $47.51   4.551%   $49.6722   $49.67   $49.65   $49.70  
  Purchase #3 $122.34   7.164%   $131.1044   $131.10   $131.10   $131.10  
  Purchase #4 $24.65   8.203%   $26.672   $26.67   $26.65   $26.70  
  Purchase #5 $205.37   13.723%   $233.5529   $233.55   $233.55   $233.60  
  Purchase #6 $48.63   9.458%   $53.2294   $53.23   $53.25   $53.20  
  Purchase #7 $240.56   6.402%   $255.9607   $255.96   $255.95   $256.00  
  7 purchase totals = $744.53       $811.9197   $811.91   $811.90   $812.00