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	$20.87	12.191%	$23.4143	$23.41	$23.40	$23.40
Purchase #2	$115.38	6.689%	$123.0978	$123.10	$123.10	$123.10
Purchase #3	$188.29	4.503%	$196.7687	$196.77	$196.75	$196.80
Purchase #4	$103.64	11.434%	$115.4902	$115.49	$115.50	$115.50
Purchase #5	$166.99	3.194%	$172.3237	$172.32	$172.30	$172.30
Purchase #6	$173.62	11.648%	$193.8433	$193.84	$193.85	$193.80
Purchase #7	$158.49	13.716%	$180.2285	$180.23	$180.25	$180.20
7 purchase totals =	$927.28		$1,005.1665	$1,005.16	$1,005.15	$1,005.10