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	$102.50	6.826%	$109.4967	$109.50	$109.50	$109.50
Purchase #2	$9.69	11.692%	$10.823	$10.82	$10.80	$10.80
Purchase #3	$43.98	12.525%	$49.4885	$49.49	$49.50	$49.50
Purchase #4	$69.54	3.531%	$71.9955	$72.00	$72.00	$72.00
Purchase #5	$75.53	3.505%	$78.1773	$78.18	$78.20	$78.20
Purchase #6	$83.65	5.519%	$88.2666	$88.27	$88.25	$88.30
Purchase #7	$120.79	13.536%	$137.1401	$137.14	$137.15	$137.10
7 purchase totals =	$505.68		$545.3877	$545.40	$545.40	$545.40