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	$173.42	8.615%	$188.3601	$188.36	$188.35	$188.40
Purchase #2	$178.44	10.300%	$196.8193	$196.82	$196.80	$196.80
Purchase #3	$216.39	7.171%	$231.9073	$231.91	$231.90	$231.90
Purchase #4	$188.49	3.362%	$194.827	$194.83	$194.85	$194.80
Purchase #5	$230.82	4.624%	$241.4931	$241.49	$241.50	$241.50
Purchase #6	$87.78	3.732%	$91.0559	$91.06	$91.05	$91.10
Purchase #7	$10.57	7.704%	$11.3843	$11.38	$11.40	$11.40
7 purchase totals =	$1,085.91		$1,155.8470	$1,155.85	$1,155.85	$1,155.90