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	$50.72	12.115%	$56.8647	$56.86	$56.85	$56.90
Purchase #2	$234.44	8.750%	$254.9535	$254.95	$254.95	$255.00
Purchase #3	$115.99	13.195%	$131.2949	$131.29	$131.30	$131.30
Purchase #4	$138.93	9.735%	$152.4548	$152.45	$152.45	$152.50
Purchase #5	$175.46	11.715%	$196.0151	$196.02	$196.00	$196.00
Purchase #6	$32.35	3.284%	$33.4124	$33.41	$33.40	$33.40
Purchase #7	$178.93	5.161%	$188.1646	$188.16	$188.15	$188.20
7 purchase totals =	$926.82		$1,013.1600	$1,013.14	$1,013.10	$1,013.30