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 $180.71   6.783%   $192.9676   $192.97   $192.95   $193.00  
  Purchase #2 $233.39   11.847%   $261.0397   $261.04   $261.05   $261.00  
  Purchase #3 $61.71   6.828%   $65.9236   $65.92   $65.90   $65.90  
  Purchase #4 $69.80   3.660%   $72.3547   $72.35   $72.35   $72.40  
  Purchase #5 $150.55   5.237%   $158.4343   $158.43   $158.45   $158.40  
  Purchase #6 $112.33   4.452%   $117.3309   $117.33   $117.35   $117.30  
  Purchase #7 $236.62   12.675%   $266.6116   $266.61   $266.60   $266.60  
  7 purchase totals = $1,045.11       $1,134.6624   $1,134.65   $1,134.65   $1,134.60