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	$40.49	3.583%	$41.9408	$41.94	$41.95	$41.90
Purchase #2	$111.46	4.517%	$116.4946	$116.49	$116.50	$116.50
Purchase #3	$19.56	13.274%	$22.1564	$22.16	$22.15	$22.20
Purchase #4	$126.53	6.352%	$134.5672	$134.57	$134.55	$134.60
Purchase #5	$249.74	11.672%	$278.8897	$278.89	$278.90	$278.90
Purchase #6	$138.70	10.154%	$152.7836	$152.78	$152.80	$152.80
Purchase #7	$78.45	13.720%	$89.2133	$89.21	$89.20	$89.20
7 purchase totals =	$764.93		$836.0456	$836.04	$836.05	$836.10