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 $57.75   13.608%   $65.6086   $65.61   $65.60   $65.60  
  Purchase #2 $95.74   4.521%   $100.0684   $100.07   $100.05   $100.10  
  Purchase #3 $41.25   4.866%   $43.2572   $43.26   $43.25   $43.30  
  Purchase #4 $182.42   6.328%   $193.9635   $193.96   $193.95   $194.00  
  Purchase #5 $220.74   11.406%   $245.9176   $245.92   $245.90   $245.90  
  Purchase #6 $220.90   9.543%   $241.9805   $241.98   $242.00   $242.00  
  Purchase #7 $67.33   5.406%   $70.9699   $70.97   $70.95   $71.00  
  7 purchase totals = $886.13       $961.7657   $961.77   $961.70   $961.90