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	$149.91	12.584%	$168.7747	$168.77	$168.75	$168.80
Purchase #2	$192.57	10.242%	$212.293	$212.29	$212.30	$212.30
Purchase #3	$128.50	12.261%	$144.2554	$144.26	$144.25	$144.30
Purchase #4	$105.36	12.243%	$118.2592	$118.26	$118.25	$118.30
Purchase #5	$167.86	6.627%	$178.9841	$178.98	$179.00	$179.00
Purchase #6	$219.98	11.717%	$245.7551	$245.76	$245.75	$245.80
Purchase #7	$118.61	7.712%	$127.7572	$127.76	$127.75	$127.80
7 purchase totals =	$1,082.79		$1,196.0787	$1,196.08	$1,196.05	$1,196.30