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	$202.74	13.701%	$230.5174	$230.52	$230.50	$230.50
Purchase #2	$80.99	10.235%	$89.2793	$89.28	$89.30	$89.30
Purchase #3	$173.33	13.553%	$196.8214	$196.82	$196.80	$196.80
Purchase #4	$170.83	4.577%	$178.6489	$178.65	$178.65	$178.60
Purchase #5	$68.35	4.370%	$71.3369	$71.34	$71.35	$71.30
Purchase #6	$38.42	11.213%	$42.728	$42.73	$42.75	$42.70
Purchase #7	$47.34	11.713%	$52.8849	$52.88	$52.90	$52.90
7 purchase totals =	$782.00		$862.2168	$862.22	$862.25	$862.10