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	$126.82	11.437%	$141.3244	$141.32	$141.30	$141.30
Purchase #2	$130.76	13.814%	$148.8232	$148.82	$148.80	$148.80
Purchase #3	$39.33	5.332%	$41.4271	$41.43	$41.45	$41.40
Purchase #4	$221.51	3.761%	$229.841	$229.84	$229.85	$229.80
Purchase #5	$106.85	4.463%	$111.6187	$111.62	$111.60	$111.60
Purchase #6	$18.56	13.473%	$21.0606	$21.06	$21.05	$21.10
Purchase #7	$100.42	6.131%	$106.5768	$106.58	$106.60	$106.60
7 purchase totals =	$744.25		$800.6718	$800.67	$800.65	$800.60