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	$92.77	7.793%	$99.9996	$100.00	$100.00	$100.00
Purchase #2	$165.25	3.859%	$171.627	$171.63	$171.65	$171.60
Purchase #3	$244.76	3.608%	$253.5909	$253.59	$253.60	$253.60
Purchase #4	$233.77	10.536%	$258.4	$258.40	$258.40	$258.40
Purchase #5	$184.73	6.187%	$196.1592	$196.16	$196.15	$196.20
Purchase #6	$99.43	9.690%	$109.0648	$109.06	$109.05	$109.10
Purchase #7	$222.83	5.514%	$235.1168	$235.12	$235.10	$235.10
7 purchase totals =	$1,243.54		$1,323.9583	$1,323.96	$1,323.95	$1,324.00