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	$149.40	10.749%	$165.459	$165.46	$165.45	$165.50
Purchase #2	$77.49	6.760%	$82.7283	$82.73	$82.75	$82.70
Purchase #3	$17.80	13.207%	$20.1508	$20.15	$20.15	$20.20
Purchase #4	$217.98	10.361%	$240.5649	$240.56	$240.55	$240.60
Purchase #5	$24.32	5.111%	$25.563	$25.56	$25.55	$25.60
Purchase #6	$40.35	7.559%	$43.4001	$43.40	$43.40	$43.40
Purchase #7	$9.78	12.218%	$10.9749	$10.97	$10.95	$11.00
7 purchase totals =	$537.12		$588.8410	$588.83	$588.80	$589.00