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	$102.46	4.823%	$107.4016	$107.40	$107.40	$107.40
Purchase #2	$233.89	9.851%	$256.9305	$256.93	$256.95	$256.90
Purchase #3	$110.28	11.739%	$123.2258	$123.23	$123.25	$123.20
Purchase #4	$207.83	4.569%	$217.3258	$217.33	$217.35	$217.30
Purchase #5	$215.97	8.544%	$234.4225	$234.42	$234.40	$234.40
Purchase #6	$53.69	11.555%	$59.8939	$59.89	$59.90	$59.90
Purchase #7	$149.88	5.857%	$158.6585	$158.66	$158.65	$158.70
7 purchase totals =	$1,074.00		$1,157.8586	$1,157.86	$1,157.90	$1,157.80