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	$17.95	11.335%	$19.9846	$19.98	$20.00	$20.00
Purchase #2	$144.91	9.218%	$158.2678	$158.27	$158.25	$158.30
Purchase #3	$120.69	7.822%	$130.1304	$130.13	$130.15	$130.10
Purchase #4	$81.84	12.587%	$92.1412	$92.14	$92.15	$92.10
Purchase #5	$183.76	9.326%	$200.8975	$200.90	$200.90	$200.90
Purchase #6	$189.45	3.581%	$196.2342	$196.23	$196.25	$196.20
Purchase #7	$70.65	11.571%	$78.8249	$78.82	$78.80	$78.80
7 purchase totals =	$809.25		$876.4806	$876.47	$876.50	$876.40