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 $75.66   13.733%   $86.0504   $86.05   $86.05   $86.10  
  Purchase #2 $17.45   13.117%   $19.7389   $19.74   $19.75   $19.70  
  Purchase #3 $155.42   5.499%   $163.9665   $163.97   $163.95   $164.00  
  Purchase #4 $246.71   10.872%   $273.5323   $273.53   $273.55   $273.50  
  Purchase #5 $170.50   13.779%   $193.9932   $193.99   $194.00   $194.00  
  Purchase #6 $223.38   10.727%   $247.342   $247.34   $247.35   $247.30  
  Purchase #7 $214.95   13.342%   $243.6286   $243.63   $243.65   $243.60  
  7 purchase totals = $1,104.07       $1,228.2519   $1,228.25   $1,228.30   $1,228.20