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 $162.97   6.170%   $173.0252   $173.03   $173.05   $173.00  
  Purchase #2 $36.60   5.698%   $38.6855   $38.69   $38.70   $38.70  
  Purchase #3 $215.26   5.728%   $227.5901   $227.59   $227.60   $227.60  
  Purchase #4 $228.54   7.460%   $245.5891   $245.59   $245.60   $245.60  
  Purchase #5 $148.68   3.575%   $153.9953   $154.00   $154.00   $154.00  
  Purchase #6 $22.42   12.178%   $25.1503   $25.15   $25.15   $25.20  
  Purchase #7 $57.51   7.698%   $61.9371   $61.94   $61.95   $61.90  
  7 purchase totals = $871.98       $925.9726   $925.99   $926.05   $926.00