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	$81.89	8.849%	$89.1364	$89.14	$89.15	$89.10
Purchase #2	$37.26	12.116%	$41.7744	$41.77	$41.75	$41.80
Purchase #3	$46.99	11.423%	$52.3577	$52.36	$52.35	$52.40
Purchase #4	$196.89	11.406%	$219.3473	$219.35	$219.35	$219.30
Purchase #5	$173.25	4.567%	$181.1623	$181.16	$181.15	$181.20
Purchase #6	$157.79	11.288%	$175.6013	$175.60	$175.60	$175.60
Purchase #7	$189.84	11.218%	$211.1363	$211.14	$211.15	$211.10
7 purchase totals =	$883.91		$970.5157	$970.52	$970.50	$970.50