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	$32.33	4.657%	$33.8356	$33.84	$33.85	$33.80
Purchase #2	$40.61	12.537%	$45.7013	$45.70	$45.70	$45.70
Purchase #3	$233.48	4.679%	$244.4045	$244.40	$244.40	$244.40
Purchase #4	$184.88	11.196%	$205.5792	$205.58	$205.60	$205.60
Purchase #5	$112.84	5.812%	$119.3983	$119.40	$119.40	$119.40
Purchase #6	$62.54	7.225%	$67.0585	$67.06	$67.05	$67.10
Purchase #7	$100.45	9.673%	$110.1665	$110.17	$110.15	$110.20
7 purchase totals =	$767.13		$826.1439	$826.15	$826.15	$826.20