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	$19.29	5.190%	$20.2912	$20.29	$20.30	$20.30
Purchase #2	$205.53	12.711%	$231.6549	$231.65	$231.65	$231.70
Purchase #3	$118.91	12.800%	$134.1305	$134.13	$134.15	$134.10
Purchase #4	$96.38	4.229%	$100.4559	$100.46	$100.45	$100.50
Purchase #5	$117.67	11.288%	$130.9526	$130.95	$130.95	$131.00
Purchase #6	$109.26	10.390%	$120.6121	$120.61	$120.60	$120.60
Purchase #7	$16.72	11.400%	$18.6261	$18.63	$18.65	$18.60
7 purchase totals =	$683.76		$756.7233	$756.72	$756.75	$756.80