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	$156.57	5.771%	$165.6057	$165.61	$165.60	$165.60
Purchase #2	$62.67	7.227%	$67.1992	$67.20	$67.20	$67.20
Purchase #3	$77.30	12.115%	$86.6649	$86.66	$86.65	$86.70
Purchase #4	$43.85	3.223%	$45.2633	$45.26	$45.25	$45.30
Purchase #5	$181.94	6.295%	$193.3931	$193.39	$193.40	$193.40
Purchase #6	$98.72	3.322%	$101.9995	$102.00	$102.00	$102.00
Purchase #7	$18.56	11.560%	$20.7055	$20.71	$20.70	$20.70
7 purchase totals =	$639.61		$680.8312	$680.83	$680.80	$680.90