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	$32.48	3.497%	$33.6158	$33.62	$33.60	$33.60
Purchase #2	$53.97	4.191%	$56.2319	$56.23	$56.25	$56.20
Purchase #3	$201.94	13.798%	$229.8037	$229.80	$229.80	$229.80
Purchase #4	$33.43	5.548%	$35.2847	$35.28	$35.30	$35.30
Purchase #5	$156.31	7.300%	$167.7206	$167.72	$167.70	$167.70
Purchase #6	$242.54	4.263%	$252.8795	$252.88	$252.90	$252.90
Purchase #7	$43.39	5.830%	$45.9196	$45.92	$45.90	$45.90
7 purchase totals =	$764.06		$821.4558	$821.45	$821.45	$821.40