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	$229.98	11.645%	$256.7612	$256.76	$256.75	$256.80
Purchase #2	$95.96	9.130%	$104.7211	$104.72	$104.70	$104.70
Purchase #3	$217.81	12.720%	$245.5154	$245.52	$245.50	$245.50
Purchase #4	$137.37	11.646%	$153.3681	$153.37	$153.35	$153.40
Purchase #5	$120.76	10.227%	$133.1101	$133.11	$133.10	$133.10
Purchase #6	$105.47	5.515%	$111.2867	$111.29	$111.30	$111.30
Purchase #7	$139.40	9.164%	$152.1746	$152.17	$152.15	$152.20
7 purchase totals =	$1,046.75		$1,156.9372	$1,156.94	$1,156.85	$1,157.00