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	$135.76	5.633%	$143.4074	$143.41	$143.40	$143.40
Purchase #2	$107.81	9.841%	$118.4196	$118.42	$118.40	$118.40
Purchase #3	$197.92	6.743%	$211.2657	$211.27	$211.25	$211.30
Purchase #4	$56.63	13.545%	$64.3005	$64.30	$64.30	$64.30
Purchase #5	$7.78	10.358%	$8.5859	$8.59	$8.60	$8.60
Purchase #6	$89.81	11.142%	$99.8166	$99.82	$99.80	$99.80
Purchase #7	$126.47	4.151%	$131.7198	$131.72	$131.70	$131.70
7 purchase totals =	$722.18		$777.5155	$777.53	$777.45	$777.50