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	$159.95	13.443%	$181.4521	$181.45	$181.45	$181.50
Purchase #2	$234.44	8.188%	$253.6359	$253.64	$253.65	$253.60
Purchase #3	$90.86	5.435%	$95.7982	$95.80	$95.80	$95.80
Purchase #4	$33.43	7.333%	$35.8814	$35.88	$35.90	$35.90
Purchase #5	$143.79	4.223%	$149.8623	$149.86	$149.85	$149.90
Purchase #6	$17.90	12.391%	$20.118	$20.12	$20.10	$20.10
Purchase #7	$94.52	13.320%	$107.1101	$107.11	$107.10	$107.10
7 purchase totals =	$774.89		$843.8580	$843.86	$843.85	$843.90