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	$240.38	5.451%	$253.4831	$253.48	$253.50	$253.50
Purchase #2	$168.88	9.625%	$185.1347	$185.13	$185.15	$185.10
Purchase #3	$67.40	6.864%	$72.0263	$72.03	$72.05	$72.00
Purchase #4	$228.78	11.525%	$255.1469	$255.15	$255.15	$255.10
Purchase #5	$109.63	11.663%	$122.4161	$122.42	$122.40	$122.40
Purchase #6	$158.53	13.510%	$179.9474	$179.95	$179.95	$179.90
Purchase #7	$140.91	8.466%	$152.8394	$152.84	$152.85	$152.80
7 purchase totals =	$1,114.51		$1,220.9939	$1,221.00	$1,221.05	$1,220.80