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	$144.31	9.837%	$158.5058	$158.51	$158.50	$158.50
Purchase #2	$203.56	6.801%	$217.4041	$217.40	$217.40	$217.40
Purchase #3	$181.46	5.255%	$190.9957	$191.00	$191.00	$191.00
Purchase #4	$48.83	10.275%	$53.8473	$53.85	$53.85	$53.80
Purchase #5	$155.41	10.690%	$172.0233	$172.02	$172.00	$172.00
Purchase #6	$66.43	4.515%	$69.4293	$69.43	$69.45	$69.40
Purchase #7	$215.49	9.279%	$235.4853	$235.49	$235.50	$235.50
7 purchase totals =	$1,015.49		$1,097.6908	$1,097.70	$1,097.70	$1,097.60