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	$226.54	9.729%	$248.5801	$248.58	$248.60	$248.60
Purchase #2	$212.28	4.870%	$222.618	$222.62	$222.60	$222.60
Purchase #3	$233.51	7.808%	$251.7425	$251.74	$251.75	$251.70
Purchase #4	$9.92	6.510%	$10.5658	$10.57	$10.55	$10.60
Purchase #5	$236.58	13.714%	$269.0246	$269.02	$269.00	$269.00
Purchase #6	$38.49	5.119%	$40.4603	$40.46	$40.45	$40.50
Purchase #7	$42.95	6.280%	$45.6473	$45.65	$45.65	$45.60
7 purchase totals =	$1,000.27		$1,088.6386	$1,088.64	$1,088.60	$1,088.60