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	$143.77	10.377%	$158.689	$158.69	$158.70	$158.70
Purchase #2	$91.62	9.345%	$100.1819	$100.18	$100.20	$100.20
Purchase #3	$27.28	6.145%	$28.9564	$28.96	$28.95	$29.00
Purchase #4	$149.61	4.717%	$156.6671	$156.67	$156.65	$156.70
Purchase #5	$18.82	8.860%	$20.4875	$20.49	$20.50	$20.50
Purchase #6	$67.26	7.872%	$72.5547	$72.55	$72.55	$72.60
Purchase #7	$114.32	11.372%	$127.3205	$127.32	$127.30	$127.30
7 purchase totals =	$612.68		$664.8571	$664.86	$664.85	$665.00