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	$32.73	4.367%	$34.1593	$34.16	$34.15	$34.20
Purchase #2	$101.29	12.688%	$114.1417	$114.14	$114.15	$114.10
Purchase #3	$105.52	7.816%	$113.7674	$113.77	$113.75	$113.80
Purchase #4	$60.39	4.200%	$62.9264	$62.93	$62.95	$62.90
Purchase #5	$170.47	6.507%	$181.5625	$181.56	$181.55	$181.60
Purchase #6	$37.65	5.291%	$39.6421	$39.64	$39.65	$39.60
Purchase #7	$94.25	6.421%	$100.3018	$100.30	$100.30	$100.30
7 purchase totals =	$602.30		$646.5012	$646.50	$646.50	$646.50