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 $86.84   13.179%   $98.2846   $98.28   $98.30   $98.30  
  Purchase #2 $77.80   9.228%   $84.9794   $84.98   $85.00   $85.00  
  Purchase #3 $57.26   5.448%   $60.3795   $60.38   $60.40   $60.40  
  Purchase #4 $190.29   8.159%   $205.8158   $205.82   $205.80   $205.80  
  Purchase #5 $51.75   8.834%   $56.3216   $56.32   $56.30   $56.30  
  Purchase #6 $215.37   4.203%   $224.422   $224.42   $224.40   $224.40  
  Purchase #7 $239.85   7.736%   $258.4048   $258.40   $258.40   $258.40  
  7 purchase totals = $919.16       $988.6077   $988.60   $988.60   $988.60