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	$227.59	12.779%	$256.6737	$256.67	$256.65	$256.70
Purchase #2	$146.94	10.594%	$162.5068	$162.51	$162.50	$162.50
Purchase #3	$99.67	5.342%	$104.9944	$104.99	$105.00	$105.00
Purchase #4	$131.27	11.723%	$146.6588	$146.66	$146.65	$146.70
Purchase #5	$96.26	4.468%	$100.5609	$100.56	$100.55	$100.60
Purchase #6	$209.45	6.407%	$222.8695	$222.87	$222.85	$222.90
Purchase #7	$114.27	3.399%	$118.154	$118.15	$118.15	$118.20
7 purchase totals =	$1,025.45		$1,112.4181	$1,112.41	$1,112.35	$1,112.60