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	$115.88	13.475%	$131.4948	$131.49	$131.50	$131.50
Purchase #2	$110.25	4.582%	$115.3017	$115.30	$115.30	$115.30
Purchase #3	$221.94	3.706%	$230.1651	$230.17	$230.15	$230.20
Purchase #4	$177.96	3.109%	$183.4928	$183.49	$183.50	$183.50
Purchase #5	$93.96	6.319%	$99.8973	$99.90	$99.90	$99.90
Purchase #6	$91.78	9.298%	$100.3137	$100.31	$100.30	$100.30
Purchase #7	$21.37	10.849%	$23.6884	$23.69	$23.70	$23.70
7 purchase totals =	$833.14		$884.3538	$884.35	$884.35	$884.40