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 $66.47   11.148%   $73.8801   $73.88   $73.90   $73.90  
  Purchase #2 $192.71   11.313%   $214.5113   $214.51   $214.50   $214.50  
  Purchase #3 $86.47   9.394%   $94.593   $94.59   $94.60   $94.60  
  Purchase #4 $180.86   5.175%   $190.2195   $190.22   $190.20   $190.20  
  Purchase #5 $93.33   7.682%   $100.4996   $100.50   $100.50   $100.50  
  Purchase #6 $92.72   4.541%   $96.9304   $96.93   $96.95   $96.90  
  Purchase #7 $22.66   3.575%   $23.4701   $23.47   $23.45   $23.50  
  7 purchase totals = $735.22       $794.1040   $794.10   $794.10   $794.10