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	$227.27	9.480%	$248.8152	$248.82	$248.80	$248.80
Purchase #2	$214.74	13.645%	$244.0413	$244.04	$244.05	$244.00
Purchase #3	$237.46	4.792%	$248.8391	$248.84	$248.85	$248.80
Purchase #4	$155.66	11.566%	$173.6636	$173.66	$173.65	$173.70
Purchase #5	$165.46	8.709%	$179.8699	$179.87	$179.85	$179.90
Purchase #6	$131.26	10.796%	$145.4308	$145.43	$145.45	$145.40
Purchase #7	$40.66	11.356%	$45.2773	$45.28	$45.30	$45.30
7 purchase totals =	$1,172.51		$1,285.9372	$1,285.94	$1,285.95	$1,285.90