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 $68.85   9.141%   $75.1436   $75.14   $75.15   $75.10  
  Purchase #2 $101.67   6.551%   $108.3304   $108.33   $108.35   $108.30  
  Purchase #3 $118.91   6.798%   $126.9935   $126.99   $127.00   $127.00  
  Purchase #4 $177.29   9.394%   $193.9446   $193.94   $193.95   $193.90  
  Purchase #5 $18.88   7.302%   $20.2586   $20.26   $20.25   $20.30  
  Purchase #6 $113.55   4.763%   $118.9584   $118.96   $118.95   $119.00  
  Purchase #7 $47.81   5.704%   $50.5371   $50.54   $50.55   $50.50  
  7 purchase totals = $646.96       $694.1662   $694.16   $694.20   $694.10