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	$109.27	5.389%	$115.1586	$115.16	$115.15	$115.20
Purchase #2	$108.69	4.376%	$113.4463	$113.45	$113.45	$113.40
Purchase #3	$229.34	11.221%	$255.0742	$255.07	$255.05	$255.10
Purchase #4	$243.95	7.627%	$262.5561	$262.56	$262.55	$262.60
Purchase #5	$244.37	11.433%	$272.3088	$272.31	$272.30	$272.30
Purchase #6	$17.84	5.354%	$18.7952	$18.80	$18.80	$18.80
Purchase #7	$65.88	10.565%	$72.8402	$72.84	$72.85	$72.80
7 purchase totals =	$1,019.34		$1,110.1794	$1,110.19	$1,110.15	$1,110.20