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 $22.39   10.500%   $24.741   $24.74   $24.75   $24.70  
  Purchase #2 $154.79   13.453%   $175.6139   $175.61   $175.60   $175.60  
  Purchase #3 $114.34   7.130%   $122.4924   $122.49   $122.50   $122.50  
  Purchase #4 $119.82   3.551%   $124.0748   $124.07   $124.05   $124.10  
  Purchase #5 $159.25   4.621%   $166.6089   $166.61   $166.60   $166.60  
  Purchase #6 $234.59   12.243%   $263.3109   $263.31   $263.30   $263.30  
  Purchase #7 $137.56   9.337%   $150.404   $150.40   $150.40   $150.40  
  7 purchase totals = $942.74       $1,027.2459   $1,027.23   $1,027.20   $1,027.20