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	$222.33	12.226%	$249.5121	$249.51	$249.50	$249.50
Purchase #2	$139.61	13.241%	$158.0958	$158.10	$158.10	$158.10
Purchase #3	$214.55	6.152%	$227.7491	$227.75	$227.75	$227.70
Purchase #4	$136.54	8.760%	$148.5009	$148.50	$148.50	$148.50
Purchase #5	$173.81	5.530%	$183.4217	$183.42	$183.40	$183.40
Purchase #6	$56.99	12.788%	$64.2779	$64.28	$64.30	$64.30
Purchase #7	$30.50	7.706%	$32.8503	$32.85	$32.85	$32.90
7 purchase totals =	$974.33		$1,064.4078	$1,064.41	$1,064.40	$1,064.40