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	$53.61	6.773%	$57.241	$57.24	$57.25	$57.20
Purchase #2	$190.78	5.116%	$200.5403	$200.54	$200.55	$200.50
Purchase #3	$54.89	7.592%	$59.0572	$59.06	$59.05	$59.10
Purchase #4	$160.64	6.296%	$170.7539	$170.75	$170.75	$170.80
Purchase #5	$180.98	9.717%	$198.5658	$198.57	$198.55	$198.60
Purchase #6	$13.37	5.724%	$14.1353	$14.14	$14.15	$14.10
Purchase #7	$32.33	5.493%	$34.1059	$34.11	$34.10	$34.10
7 purchase totals =	$686.60		$734.3994	$734.41	$734.40	$734.40