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 $162.74   13.116%   $184.085   $184.09   $184.10   $184.10  
  Purchase #2 $183.81   6.374%   $195.526   $195.53   $195.55   $195.50  
  Purchase #3 $241.61   8.141%   $261.2795   $261.28   $261.30   $261.30  
  Purchase #4 $204.93   12.121%   $229.7696   $229.77   $229.75   $229.80  
  Purchase #5 $188.67   3.253%   $194.8074   $194.81   $194.80   $194.80  
  Purchase #6 $229.41   12.307%   $257.6435   $257.64   $257.65   $257.60  
  Purchase #7 $234.62   13.308%   $265.8432   $265.84   $265.85   $265.80  
  7 purchase totals = $1,445.79       $1,588.9542   $1,588.96   $1,589.00   $1,588.90