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 $176.54   10.491%   $195.0608   $195.06   $195.05   $195.10  
  Purchase #2 $76.87   4.867%   $80.6113   $80.61   $80.60   $80.60  
  Purchase #3 $65.87   6.270%   $70   $70.00   $70.00   $70.00  
  Purchase #4 $24.51   12.677%   $27.6171   $27.62   $27.60   $27.60  
  Purchase #5 $58.75   9.420%   $64.2843   $64.28   $64.30   $64.30  
  Purchase #6 $176.27   8.290%   $190.8828   $190.88   $190.90   $190.90  
  Purchase #7 $94.41   4.219%   $98.3932   $98.39   $98.40   $98.40  
  7 purchase totals = $673.22       $726.8495   $726.84   $726.85   $726.90