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	$110.76	12.250%	$124.3281	$124.33	$124.35	$124.30
Purchase #2	$161.56	12.525%	$181.7954	$181.80	$181.80	$181.80
Purchase #3	$127.95	12.460%	$143.8926	$143.89	$143.90	$143.90
Purchase #4	$82.90	10.431%	$91.5473	$91.55	$91.55	$91.50
Purchase #5	$10.30	13.567%	$11.6974	$11.70	$11.70	$11.70
Purchase #6	$83.74	10.460%	$92.4992	$92.50	$92.50	$92.50
Purchase #7	$9.25	12.188%	$10.3774	$10.38	$10.40	$10.40
7 purchase totals =	$586.46		$656.1374	$656.15	$656.20	$656.10