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	$18.89	9.483%	$20.6813	$20.68	$20.70	$20.70
Purchase #2	$153.95	4.406%	$160.733	$160.73	$160.75	$160.70
Purchase #3	$202.83	6.504%	$216.0221	$216.02	$216.00	$216.00
Purchase #4	$237.92	13.159%	$269.2279	$269.23	$269.25	$269.20
Purchase #5	$238.69	7.779%	$257.2577	$257.26	$257.25	$257.30
Purchase #6	$38.73	13.447%	$43.938	$43.94	$43.95	$43.90
Purchase #7	$31.28	13.343%	$35.4537	$35.45	$35.45	$35.50
7 purchase totals =	$922.29		$1,003.3137	$1,003.31	$1,003.35	$1,003.30