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	$58.88	9.578%	$64.5195	$64.52	$64.50	$64.50
Purchase #2	$118.98	7.369%	$127.7476	$127.75	$127.75	$127.70
Purchase #3	$32.68	4.551%	$34.1673	$34.17	$34.15	$34.20
Purchase #4	$112.82	10.470%	$124.6323	$124.63	$124.65	$124.60
Purchase #5	$116.83	12.381%	$131.2947	$131.29	$131.30	$131.30
Purchase #6	$225.37	11.773%	$251.9028	$251.90	$251.90	$251.90
Purchase #7	$43.53	8.769%	$47.3471	$47.35	$47.35	$47.30
7 purchase totals =	$709.09		$781.6113	$781.61	$781.60	$781.50