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	$53.30	12.215%	$59.8106	$59.81	$59.80	$59.80
Purchase #2	$82.33	8.717%	$89.5067	$89.51	$89.50	$89.50
Purchase #3	$52.34	8.589%	$56.8355	$56.84	$56.85	$56.80
Purchase #4	$110.52	12.144%	$123.9415	$123.94	$123.95	$123.90
Purchase #5	$166.75	4.667%	$174.5322	$174.53	$174.55	$174.50
Purchase #6	$204.45	13.549%	$232.1509	$232.15	$232.15	$232.20
Purchase #7	$162.69	6.472%	$173.2193	$173.22	$173.20	$173.20
7 purchase totals =	$832.38		$909.9967	$910.00	$910.00	$909.90