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	$217.98	6.122%	$231.3247	$231.32	$231.30	$231.30
Purchase #2	$73.55	4.585%	$76.9223	$76.92	$76.90	$76.90
Purchase #3	$70.55	10.752%	$78.1355	$78.14	$78.15	$78.10
Purchase #4	$37.60	11.498%	$41.9232	$41.92	$41.90	$41.90
Purchase #5	$179.51	10.731%	$198.7732	$198.77	$198.75	$198.80
Purchase #6	$117.52	10.208%	$129.5164	$129.52	$129.50	$129.50
Purchase #7	$116.98	11.218%	$130.1028	$130.10	$130.10	$130.10
7 purchase totals =	$813.69		$886.6981	$886.69	$886.60	$886.60