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 $60.87   10.591%   $67.3167   $67.32   $67.30   $67.30  
  Purchase #2 $60.77   9.175%   $66.3456   $66.35   $66.35   $66.30  
  Purchase #3 $135.76   8.453%   $147.2358   $147.24   $147.25   $147.20  
  Purchase #4 $70.26   5.797%   $74.333   $74.33   $74.35   $74.30  
  Purchase #5 $9.35   11.866%   $10.4595   $10.46   $10.45   $10.50  
  Purchase #6 $210.99   13.423%   $239.3112   $239.31   $239.30   $239.30  
  Purchase #7 $126.64   13.144%   $143.2856   $143.29   $143.30   $143.30  
  7 purchase totals = $674.64       $748.2874   $748.30   $748.30   $748.20