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	$80.57	11.305%	$89.6784	$89.68	$89.70	$89.70
Purchase #2	$157.94	8.492%	$171.3523	$171.35	$171.35	$171.40
Purchase #3	$57.33	9.678%	$62.8784	$62.88	$62.90	$62.90
Purchase #4	$240.98	4.848%	$252.6627	$252.66	$252.65	$252.70
Purchase #5	$188.42	4.113%	$196.1697	$196.17	$196.15	$196.20
Purchase #6	$69.96	9.707%	$76.751	$76.75	$76.75	$76.80
Purchase #7	$221.79	4.416%	$231.5842	$231.58	$231.60	$231.60
7 purchase totals =	$1,016.99		$1,081.0767	$1,081.07	$1,081.10	$1,081.30