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	$165.54	10.253%	$182.5128	$182.51	$182.50	$182.50
Purchase #2	$56.68	8.345%	$61.4099	$61.41	$61.40	$61.40
Purchase #3	$46.98	6.608%	$50.0844	$50.08	$50.10	$50.10
Purchase #4	$125.46	3.834%	$130.2701	$130.27	$130.25	$130.30
Purchase #5	$25.73	11.789%	$28.7633	$28.76	$28.75	$28.80
Purchase #6	$19.59	9.707%	$21.4916	$21.49	$21.50	$21.50
Purchase #7	$77.25	3.595%	$80.0271	$80.03	$80.05	$80.00
7 purchase totals =	$517.23		$554.5592	$554.55	$554.55	$554.60