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	$6.47	13.458%	$7.3407	$7.34	$7.35	$7.30
Purchase #2	$40.87	11.253%	$45.4691	$45.47	$45.45	$45.50
Purchase #3	$234.76	5.470%	$247.6014	$247.60	$247.60	$247.60
Purchase #4	$152.37	6.840%	$162.7921	$162.79	$162.80	$162.80
Purchase #5	$102.47	8.360%	$111.0365	$111.04	$111.05	$111.00
Purchase #6	$42.76	10.149%	$47.0997	$47.10	$47.10	$47.10
Purchase #7	$75.59	5.139%	$79.4746	$79.47	$79.45	$79.50
7 purchase totals =	$655.29		$700.8141	$700.81	$700.80	$700.80