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	$66.70	8.554%	$72.4055	$72.41	$72.40	$72.40
Purchase #2	$150.60	5.115%	$158.3032	$158.30	$158.30	$158.30
Purchase #3	$81.46	10.288%	$89.8406	$89.84	$89.85	$89.80
Purchase #4	$102.39	12.170%	$114.8509	$114.85	$114.85	$114.90
Purchase #5	$244.73	11.269%	$272.3086	$272.31	$272.30	$272.30
Purchase #6	$180.93	12.352%	$203.2785	$203.28	$203.30	$203.30
Purchase #7	$59.47	3.492%	$61.5467	$61.55	$61.55	$61.50
7 purchase totals =	$886.28		$972.5340	$972.54	$972.55	$972.50