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	$97.94	6.761%	$104.5617	$104.56	$104.55	$104.60
Purchase #2	$98.69	12.841%	$111.3628	$111.36	$111.35	$111.40
Purchase #3	$43.93	7.340%	$47.1545	$47.15	$47.15	$47.20
Purchase #4	$83.90	6.430%	$89.2948	$89.29	$89.30	$89.30
Purchase #5	$46.60	8.137%	$50.3918	$50.39	$50.40	$50.40
Purchase #6	$49.27	5.107%	$51.7862	$51.79	$51.80	$51.80
Purchase #7	$58.97	9.792%	$64.7443	$64.74	$64.75	$64.70
7 purchase totals =	$479.30		$519.2961	$519.28	$519.30	$519.40