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	$54.39	6.874%	$58.1288	$58.13	$58.15	$58.10
Purchase #2	$94.78	9.674%	$103.949	$103.95	$103.95	$103.90
Purchase #3	$154.97	11.186%	$172.3049	$172.30	$172.30	$172.30
Purchase #4	$40.84	3.104%	$42.1077	$42.11	$42.10	$42.10
Purchase #5	$26.76	11.506%	$29.839	$29.84	$29.85	$29.80
Purchase #6	$230.33	8.606%	$250.1522	$250.15	$250.15	$250.20
Purchase #7	$39.85	6.197%	$42.3195	$42.32	$42.30	$42.30
7 purchase totals =	$641.92		$698.8011	$698.80	$698.80	$698.70