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	$11.90	6.724%	$12.7002	$12.70	$12.70	$12.70
Purchase #2	$230.98	8.414%	$250.4147	$250.41	$250.40	$250.40
Purchase #3	$169.63	13.361%	$192.2943	$192.29	$192.30	$192.30
Purchase #4	$57.37	7.853%	$61.8753	$61.88	$61.90	$61.90
Purchase #5	$104.44	6.631%	$111.3654	$111.37	$111.35	$111.40
Purchase #6	$17.96	3.481%	$18.5852	$18.59	$18.60	$18.60
Purchase #7	$22.46	9.849%	$24.6721	$24.67	$24.65	$24.70
7 purchase totals =	$614.74		$671.9072	$671.91	$671.90	$672.00