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	$22.57	7.687%	$24.305	$24.31	$24.30	$24.30
Purchase #2	$144.41	5.861%	$152.8739	$152.87	$152.85	$152.90
Purchase #3	$203.27	4.232%	$211.8724	$211.87	$211.85	$211.90
Purchase #4	$45.64	10.726%	$50.5353	$50.54	$50.55	$50.50
Purchase #5	$188.62	10.839%	$209.0645	$209.06	$209.05	$209.10
Purchase #6	$37.54	10.406%	$41.4464	$41.45	$41.45	$41.40
Purchase #7	$93.50	3.648%	$96.9109	$96.91	$96.90	$96.90
7 purchase totals =	$735.55		$787.0084	$787.01	$786.95	$787.00