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	$145.64	13.433%	$165.2038	$165.20	$165.20	$165.20
Purchase #2	$71.54	9.867%	$78.5989	$78.60	$78.60	$78.60
Purchase #3	$91.41	13.823%	$104.0456	$104.05	$104.05	$104.00
Purchase #4	$43.91	6.518%	$46.7721	$46.77	$46.75	$46.80
Purchase #5	$233.76	5.135%	$245.7636	$245.76	$245.75	$245.80
Purchase #6	$210.55	13.206%	$238.3552	$238.36	$238.35	$238.40
Purchase #7	$171.59	12.543%	$193.1125	$193.11	$193.10	$193.10
7 purchase totals =	$968.40		$1,071.8517	$1,071.85	$1,071.80	$1,071.90