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	$248.97	4.340%	$259.7753	$259.78	$259.80	$259.80
Purchase #2	$232.75	9.829%	$255.627	$255.63	$255.65	$255.60
Purchase #3	$112.75	4.774%	$118.1327	$118.13	$118.15	$118.10
Purchase #4	$153.56	5.537%	$162.0626	$162.06	$162.05	$162.10
Purchase #5	$78.75	8.490%	$85.4359	$85.44	$85.45	$85.40
Purchase #6	$225.82	6.134%	$239.6718	$239.67	$239.65	$239.70
Purchase #7	$31.57	12.568%	$35.5377	$35.54	$35.55	$35.50
7 purchase totals =	$1,084.17		$1,156.2430	$1,156.25	$1,156.30	$1,156.20