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	$72.38	8.197%	$78.313	$78.31	$78.30	$78.30
Purchase #2	$246.57	8.117%	$266.5841	$266.58	$266.60	$266.60
Purchase #3	$121.72	5.783%	$128.7591	$128.76	$128.75	$128.80
Purchase #4	$104.99	6.198%	$111.4973	$111.50	$111.50	$111.50
Purchase #5	$125.32	7.391%	$134.5824	$134.58	$134.60	$134.60
Purchase #6	$171.58	12.827%	$193.5886	$193.59	$193.60	$193.60
Purchase #7	$37.43	4.343%	$39.0556	$39.06	$39.05	$39.10
7 purchase totals =	$879.99		$952.3801	$952.38	$952.40	$952.50