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 $238.82   10.223%   $263.2346   $263.23   $263.25   $263.20  
  Purchase #2 $150.97   10.357%   $166.606   $166.61   $166.60   $166.60  
  Purchase #3 $79.97   11.149%   $88.8859   $88.89   $88.90   $88.90  
  Purchase #4 $228.84   8.676%   $248.6942   $248.69   $248.70   $248.70  
  Purchase #5 $69.76   5.830%   $73.827   $73.83   $73.85   $73.80  
  Purchase #6 $8.98   4.449%   $9.3795   $9.38   $9.40   $9.40  
  Purchase #7 $41.29   6.534%   $43.9879   $43.99   $44.00   $44.00  
  7 purchase totals = $818.63       $894.6151   $894.62   $894.70   $894.60