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	$120.51	13.333%	$136.5776	$136.58	$136.60	$136.60
Purchase #2	$60.78	6.621%	$64.8042	$64.80	$64.80	$64.80
Purchase #3	$223.25	8.658%	$242.579	$242.58	$242.60	$242.60
Purchase #4	$84.68	12.717%	$95.4488	$95.45	$95.45	$95.40
Purchase #5	$87.78	11.558%	$97.9256	$97.93	$97.95	$97.90
Purchase #6	$99.72	11.717%	$111.4042	$111.40	$111.40	$111.40
Purchase #7	$213.39	4.415%	$222.8112	$222.81	$222.80	$222.80
7 purchase totals =	$890.11		$971.5506	$971.55	$971.60	$971.50