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	$109.55	13.145%	$123.9503	$123.95	$123.95	$124.00
Purchase #2	$51.65	5.235%	$54.3539	$54.35	$54.35	$54.40
Purchase #3	$197.27	11.494%	$219.9442	$219.94	$219.95	$219.90
Purchase #4	$210.60	10.701%	$233.1363	$233.14	$233.15	$233.10
Purchase #5	$24.64	10.797%	$27.3004	$27.30	$27.30	$27.30
Purchase #6	$158.44	6.617%	$168.924	$168.92	$168.90	$168.90
Purchase #7	$64.52	10.575%	$71.343	$71.34	$71.35	$71.30
7 purchase totals =	$816.67		$898.9521	$898.94	$898.95	$898.90