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	$39.30	3.652%	$40.7352	$40.74	$40.75	$40.70
Purchase #2	$104.75	6.491%	$111.5493	$111.55	$111.55	$111.50
Purchase #3	$53.41	9.203%	$58.3253	$58.33	$58.35	$58.30
Purchase #4	$94.99	13.804%	$108.1024	$108.10	$108.10	$108.10
Purchase #5	$54.71	7.268%	$58.6863	$58.69	$58.70	$58.70
Purchase #6	$100.46	8.327%	$108.8253	$108.83	$108.85	$108.80
Purchase #7	$105.50	4.188%	$109.9183	$109.92	$109.90	$109.90
7 purchase totals =	$553.12		$596.1421	$596.16	$596.20	$596.00