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	$104.28	6.684%	$111.2501	$111.25	$111.25	$111.30
Purchase #2	$193.77	12.242%	$217.4913	$217.49	$217.50	$217.50
Purchase #3	$88.74	3.810%	$92.121	$92.12	$92.10	$92.10
Purchase #4	$173.67	9.466%	$190.1096	$190.11	$190.10	$190.10
Purchase #5	$39.48	10.806%	$43.7462	$43.75	$43.75	$43.70
Purchase #6	$150.96	11.629%	$168.5151	$168.52	$168.50	$168.50
Purchase #7	$40.41	13.190%	$45.7401	$45.74	$45.75	$45.70
7 purchase totals =	$791.31		$868.9734	$868.98	$868.95	$868.90