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	$87.41	5.140%	$91.9029	$91.90	$91.90	$91.90
Purchase #2	$93.91	11.163%	$104.3932	$104.39	$104.40	$104.40
Purchase #3	$237.38	4.245%	$247.4568	$247.46	$247.45	$247.50
Purchase #4	$245.86	5.274%	$258.8267	$258.83	$258.85	$258.80
Purchase #5	$159.61	12.358%	$179.3346	$179.33	$179.35	$179.30
Purchase #6	$222.80	3.636%	$230.901	$230.90	$230.90	$230.90
Purchase #7	$60.61	8.388%	$65.694	$65.69	$65.70	$65.70
7 purchase totals =	$1,107.58		$1,178.5092	$1,178.50	$1,178.55	$1,178.50