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	$49.74	9.145%	$54.2887	$54.29	$54.30	$54.30
Purchase #2	$5.69	12.410%	$6.3961	$6.40	$6.40	$6.40
Purchase #3	$249.59	12.326%	$280.3545	$280.35	$280.35	$280.40
Purchase #4	$169.37	9.286%	$185.0977	$185.10	$185.10	$185.10
Purchase #5	$126.33	12.148%	$141.6766	$141.68	$141.70	$141.70
Purchase #6	$107.56	3.310%	$111.1202	$111.12	$111.10	$111.10
Purchase #7	$120.52	11.237%	$134.0628	$134.06	$134.05	$134.10
7 purchase totals =	$828.80		$912.9966	$913.00	$913.00	$913.10