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	$234.27	5.548%	$247.2673	$247.27	$247.25	$247.30
Purchase #2	$117.57	4.333%	$122.6643	$122.66	$122.65	$122.70
Purchase #3	$124.68	5.323%	$131.3167	$131.32	$131.30	$131.30
Purchase #4	$88.32	11.261%	$98.2657	$98.27	$98.25	$98.30
Purchase #5	$166.57	8.162%	$180.1654	$180.17	$180.15	$180.20
Purchase #6	$17.87	3.621%	$18.5171	$18.52	$18.50	$18.50
Purchase #7	$123.26	3.417%	$127.4718	$127.47	$127.45	$127.50
7 purchase totals =	$872.54		$925.6683	$925.68	$925.55	$925.80