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	$57.49	3.353%	$59.4176	$59.42	$59.40	$59.40
Purchase #2	$109.27	6.617%	$116.5004	$116.50	$116.50	$116.50
Purchase #3	$109.57	7.481%	$117.7669	$117.77	$117.75	$117.80
Purchase #4	$105.81	12.346%	$118.8733	$118.87	$118.85	$118.90
Purchase #5	$30.90	5.367%	$32.5584	$32.56	$32.55	$32.60
Purchase #6	$231.37	10.432%	$255.5065	$255.51	$255.50	$255.50
Purchase #7	$90.82	6.437%	$96.6661	$96.67	$96.65	$96.70
7 purchase totals =	$735.23		$797.2892	$797.30	$797.20	$797.40