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	$11.49	9.618%	$12.5951	$12.60	$12.60	$12.60
Purchase #2	$40.47	12.275%	$45.4377	$45.44	$45.45	$45.40
Purchase #3	$166.47	10.380%	$183.7496	$183.75	$183.75	$183.70
Purchase #4	$55.74	9.159%	$60.8452	$60.85	$60.85	$60.80
Purchase #5	$57.37	4.104%	$59.7245	$59.72	$59.70	$59.70
Purchase #6	$102.76	9.711%	$112.739	$112.74	$112.75	$112.70
Purchase #7	$78.71	12.542%	$88.5818	$88.58	$88.60	$88.60
7 purchase totals =	$513.01		$563.6729	$563.68	$563.70	$563.50