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	$202.91	9.312%	$221.805	$221.81	$221.80	$221.80
Purchase #2	$109.80	8.766%	$119.4251	$119.43	$119.45	$119.40
Purchase #3	$39.94	6.272%	$42.445	$42.45	$42.45	$42.40
Purchase #4	$93.76	3.367%	$96.9169	$96.92	$96.90	$96.90
Purchase #5	$206.27	6.793%	$220.2819	$220.28	$220.30	$220.30
Purchase #6	$97.69	13.679%	$111.053	$111.05	$111.05	$111.10
Purchase #7	$238.64	11.598%	$266.3175	$266.32	$266.30	$266.30
7 purchase totals =	$989.01		$1,078.2444	$1,078.26	$1,078.25	$1,078.20