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 $54.43   10.383%   $60.0815   $60.08   $60.10   $60.10  
  Purchase #2 $155.43   6.798%   $165.9961   $166.00   $166.00   $166.00  
  Purchase #3 $76.57   3.194%   $79.0156   $79.02   $79.00   $79.00  
  Purchase #4 $144.65   12.181%   $162.2698   $162.27   $162.25   $162.30  
  Purchase #5 $185.37   12.204%   $207.9926   $207.99   $208.00   $208.00  
  Purchase #6 $195.77   5.719%   $206.9661   $206.97   $206.95   $207.00  
  Purchase #7 $176.76   9.754%   $194.0012   $194.00   $194.00   $194.00  
  7 purchase totals = $988.98       $1,076.3229   $1,076.33   $1,076.30   $1,076.40