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	$122.71	4.360%	$128.0602	$128.06	$128.05	$128.10
Purchase #2	$74.90	5.412%	$78.9536	$78.95	$78.95	$79.00
Purchase #3	$52.59	9.656%	$57.6681	$57.67	$57.65	$57.70
Purchase #4	$188.62	5.644%	$199.2657	$199.27	$199.25	$199.30
Purchase #5	$205.35	9.145%	$224.1293	$224.13	$224.15	$224.10
Purchase #6	$143.30	3.817%	$148.7698	$148.77	$148.75	$148.80
Purchase #7	$146.38	13.857%	$166.6639	$166.66	$166.65	$166.70
7 purchase totals =	$933.85		$1,003.5106	$1,003.51	$1,003.45	$1,003.70