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	$155.48	6.423%	$165.4665	$165.47	$165.45	$165.50
Purchase #2	$244.98	8.853%	$266.6681	$266.67	$266.65	$266.70
Purchase #3	$30.64	7.108%	$32.8179	$32.82	$32.80	$32.80
Purchase #4	$17.35	4.503%	$18.1313	$18.13	$18.15	$18.10
Purchase #5	$24.43	13.519%	$27.7327	$27.73	$27.75	$27.70
Purchase #6	$99.59	9.621%	$109.1716	$109.17	$109.15	$109.20
Purchase #7	$99.46	11.493%	$110.8909	$110.89	$110.90	$110.90
7 purchase totals =	$671.93		$730.8790	$730.88	$730.85	$730.90