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	$24.87	10.373%	$27.4498	$27.45	$27.45	$27.40
Purchase #2	$88.66	9.118%	$96.744	$96.74	$96.75	$96.70
Purchase #3	$233.50	9.470%	$255.6125	$255.61	$255.60	$255.60
Purchase #4	$38.52	5.541%	$40.6544	$40.65	$40.65	$40.70
Purchase #5	$136.44	6.834%	$145.7643	$145.76	$145.75	$145.80
Purchase #6	$38.54	11.419%	$42.9409	$42.94	$42.95	$42.90
Purchase #7	$143.45	5.510%	$151.3541	$151.35	$151.35	$151.40
7 purchase totals =	$703.98		$760.5200	$760.50	$760.50	$760.50