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	$19.40	9.479%	$21.2389	$21.24	$21.25	$21.20
Purchase #2	$26.80	4.160%	$27.9149	$27.91	$27.90	$27.90
Purchase #3	$31.61	12.321%	$35.5047	$35.50	$35.50	$35.50
Purchase #4	$43.53	3.117%	$44.8868	$44.89	$44.90	$44.90
Purchase #5	$6.57	6.543%	$6.9999	$7.00	$7.00	$7.00
Purchase #6	$123.55	11.260%	$137.4617	$137.46	$137.45	$137.50
Purchase #7	$146.30	10.793%	$162.0902	$162.09	$162.10	$162.10
7 purchase totals =	$397.76		$436.0971	$436.09	$436.10	$436.10