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	$71.57	12.828%	$80.751	$80.75	$80.75	$80.80
Purchase #2	$106.60	11.337%	$118.6852	$118.69	$118.70	$118.70
Purchase #3	$177.66	5.102%	$186.7242	$186.72	$186.70	$186.70
Purchase #4	$36.29	10.128%	$39.9655	$39.97	$39.95	$40.00
Purchase #5	$8.96	13.370%	$10.158	$10.16	$10.15	$10.20
Purchase #6	$49.37	9.269%	$53.9461	$53.95	$53.95	$53.90
Purchase #7	$41.86	9.222%	$45.7203	$45.72	$45.70	$45.70
7 purchase totals =	$492.31		$535.9503	$535.96	$535.90	$536.00