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	$146.77	13.279%	$166.2596	$166.26	$166.25	$166.30
Purchase #2	$49.27	6.715%	$52.5785	$52.58	$52.60	$52.60
Purchase #3	$171.64	5.160%	$180.4966	$180.50	$180.50	$180.50
Purchase #4	$165.63	3.494%	$171.4171	$171.42	$171.40	$171.40
Purchase #5	$230.27	8.675%	$250.2459	$250.25	$250.25	$250.20
Purchase #6	$186.97	11.264%	$208.0303	$208.03	$208.05	$208.00
Purchase #7	$62.39	13.731%	$70.9568	$70.96	$70.95	$71.00
7 purchase totals =	$1,012.94		$1,099.9848	$1,100.00	$1,100.00	$1,100.00