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 $188.62   3.345%   $194.9293   $194.93   $194.95   $194.90  
  Purchase #2 $223.62   4.845%   $234.4544   $234.45   $234.45   $234.50  
  Purchase #3 $153.72   5.443%   $162.087   $162.09   $162.10   $162.10  
  Purchase #4 $69.53   6.296%   $73.9076   $73.91   $73.90   $73.90  
  Purchase #5 $244.29   9.711%   $268.013   $268.01   $268.00   $268.00  
  Purchase #6 $26.81   4.141%   $27.9202   $27.92   $27.90   $27.90  
  Purchase #7 $224.33   5.608%   $236.9104   $236.91   $236.90   $236.90  
  7 purchase totals = $1,130.92       $1,198.2219   $1,198.22   $1,198.20   $1,198.20