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 $233.40   5.269%   $245.6978   $245.70   $245.70   $245.70  
  Purchase #2 $149.93   11.358%   $166.959   $166.96   $166.95   $167.00  
  Purchase #3 $206.84   13.239%   $234.2235   $234.22   $234.20   $234.20  
  Purchase #4 $29.82   12.523%   $33.5544   $33.55   $33.55   $33.60  
  Purchase #5 $185.92   4.457%   $194.2065   $194.21   $194.20   $194.20  
  Purchase #6 $9.64   13.719%   $10.9625   $10.96   $10.95   $11.00  
  Purchase #7 $151.72   11.306%   $168.8735   $168.87   $168.85   $168.90  
  7 purchase totals = $967.27       $1,054.4772   $1,054.47   $1,054.40   $1,054.60