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 $147.82   10.242%   $162.9597   $162.96   $162.95   $163.00  
  Purchase #2 $50.60   5.561%   $53.4139   $53.41   $53.40   $53.40  
  Purchase #3 $100.40   12.496%   $112.946   $112.95   $112.95   $112.90  
  Purchase #4 $19.85   10.215%   $21.8777   $21.88   $21.90   $21.90  
  Purchase #5 $67.61   4.594%   $70.716   $70.72   $70.70   $70.70  
  Purchase #6 $190.66   6.526%   $203.1025   $203.10   $203.10   $203.10  
  Purchase #7 $117.62   5.431%   $124.0079   $124.01   $124.00   $124.00  
  7 purchase totals = $694.56       $749.0237   $749.03   $749.00   $749.00