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	$153.90	3.649%	$159.5158	$159.52	$159.50	$159.50
Purchase #2	$173.53	8.418%	$188.1378	$188.14	$188.15	$188.10
Purchase #3	$250.66	12.412%	$281.7719	$281.77	$281.75	$281.80
Purchase #4	$142.25	9.756%	$156.1279	$156.13	$156.15	$156.10
Purchase #5	$187.73	4.771%	$196.6866	$196.69	$196.70	$196.70
Purchase #6	$196.27	4.286%	$204.6821	$204.68	$204.70	$204.70
Purchase #7	$133.99	9.210%	$146.3305	$146.33	$146.35	$146.30
7 purchase totals =	$1,238.33		$1,333.2526	$1,333.26	$1,333.30	$1,333.20