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	$51.66	4.708%	$54.0922	$54.09	$54.10	$54.10
Purchase #2	$222.99	5.641%	$235.5689	$235.57	$235.55	$235.60
Purchase #3	$138.70	8.478%	$150.459	$150.46	$150.45	$150.50
Purchase #4	$41.53	3.135%	$42.832	$42.83	$42.85	$42.80
Purchase #5	$43.56	11.712%	$48.6617	$48.66	$48.65	$48.70
Purchase #6	$40.91	10.657%	$45.2698	$45.27	$45.25	$45.30
Purchase #7	$56.73	5.839%	$60.0425	$60.04	$60.05	$60.00
7 purchase totals =	$596.08		$636.9261	$636.92	$636.90	$637.00