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 $68.80   8.414%   $74.5888   $74.59   $74.60   $74.60  
  Purchase #2 $25.48   9.528%   $27.9077   $27.91   $27.90   $27.90  
  Purchase #3 $166.55   4.103%   $173.3835   $173.38   $173.40   $173.40  
  Purchase #4 $58.46   11.765%   $65.3378   $65.34   $65.35   $65.30  
  Purchase #5 $103.25   4.258%   $107.6464   $107.65   $107.65   $107.60  
  Purchase #6 $125.91   12.694%   $141.893   $141.89   $141.90   $141.90  
  Purchase #7 $206.91   12.718%   $233.2248   $233.22   $233.20   $233.20  
  7 purchase totals = $755.36       $823.9820   $823.98   $824.00   $823.90