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	$81.62	13.107%	$92.3179	$92.32	$92.30	$92.30
Purchase #2	$34.27	8.659%	$37.2374	$37.24	$37.25	$37.20
Purchase #3	$61.44	6.299%	$65.3101	$65.31	$65.30	$65.30
Purchase #4	$230.48	10.852%	$255.4917	$255.49	$255.50	$255.50
Purchase #5	$93.69	5.384%	$98.7343	$98.73	$98.75	$98.70
Purchase #6	$31.47	9.463%	$34.448	$34.45	$34.45	$34.40
Purchase #7	$247.34	8.261%	$267.7728	$267.77	$267.75	$267.80
7 purchase totals =	$780.31		$851.3122	$851.31	$851.30	$851.20