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	$166.50	13.464%	$188.9176	$188.92	$188.90	$188.90
Purchase #2	$30.33	5.722%	$32.0655	$32.07	$32.05	$32.10
Purchase #3	$149.47	4.558%	$156.2828	$156.28	$156.30	$156.30
Purchase #4	$240.76	10.233%	$265.397	$265.40	$265.40	$265.40
Purchase #5	$110.52	9.223%	$120.7133	$120.71	$120.70	$120.70
Purchase #6	$222.29	5.133%	$233.7001	$233.70	$233.70	$233.70
Purchase #7	$131.96	10.431%	$145.7247	$145.72	$145.70	$145.70
7 purchase totals =	$1,051.83		$1,142.8010	$1,142.80	$1,142.75	$1,142.80