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	$62.64	11.714%	$69.9776	$69.98	$70.00	$70.00
Purchase #2	$175.81	7.763%	$189.4581	$189.46	$189.45	$189.50
Purchase #3	$187.45	8.705%	$203.7675	$203.77	$203.75	$203.80
Purchase #4	$12.50	3.334%	$12.9168	$12.92	$12.90	$12.90
Purchase #5	$164.74	4.731%	$172.5338	$172.53	$172.55	$172.50
Purchase #6	$192.91	13.806%	$219.5432	$219.54	$219.55	$219.50
Purchase #7	$53.96	9.671%	$59.1785	$59.18	$59.20	$59.20
7 purchase totals =	$850.01		$927.3755	$927.38	$927.40	$927.40