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	$74.32	5.657%	$78.5243	$78.52	$78.50	$78.50
Purchase #2	$181.53	5.478%	$191.4742	$191.47	$191.45	$191.50
Purchase #3	$249.45	5.794%	$263.9031	$263.90	$263.90	$263.90
Purchase #4	$219.59	13.638%	$249.5377	$249.54	$249.55	$249.50
Purchase #5	$169.85	8.157%	$183.7047	$183.70	$183.70	$183.70
Purchase #6	$238.30	3.788%	$247.3268	$247.33	$247.35	$247.30
Purchase #7	$210.30	4.679%	$220.1399	$220.14	$220.15	$220.10
7 purchase totals =	$1,343.34		$1,434.6107	$1,434.60	$1,434.60	$1,434.50