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 $94.42   4.398%   $98.5726   $98.57   $98.55   $98.60  
  Purchase #2 $185.87   6.147%   $197.2954   $197.30   $197.30   $197.30  
  Purchase #3 $74.84   8.731%   $81.3743   $81.37   $81.35   $81.40  
  Purchase #4 $127.93   12.139%   $143.4594   $143.46   $143.45   $143.50  
  Purchase #5 $191.74   4.672%   $200.6981   $200.70   $200.70   $200.70  
  Purchase #6 $91.43   3.261%   $94.4115   $94.41   $94.40   $94.40  
  Purchase #7 $57.97   12.548%   $65.2441   $65.24   $65.25   $65.20  
  7 purchase totals = $824.20       $881.0554   $881.05   $881.00   $881.10