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	$96.53	4.251%	$100.6335	$100.63	$100.65	$100.60
Purchase #2	$248.66	13.162%	$281.3886	$281.39	$281.40	$281.40
Purchase #3	$161.33	13.300%	$182.7869	$182.79	$182.80	$182.80
Purchase #4	$141.47	11.841%	$158.2215	$158.22	$158.20	$158.20
Purchase #5	$111.30	8.325%	$120.5657	$120.57	$120.55	$120.60
Purchase #6	$136.72	3.677%	$141.7472	$141.75	$141.75	$141.70
Purchase #7	$93.53	10.818%	$103.6481	$103.65	$103.65	$103.60
7 purchase totals =	$989.54		$1,088.9915	$1,089.00	$1,089.00	$1,088.90