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	$25.47	9.204%	$27.8143	$27.81	$27.80	$27.80
Purchase #2	$10.90	8.313%	$11.8061	$11.81	$11.80	$11.80
Purchase #3	$221.61	13.317%	$251.1218	$251.12	$251.10	$251.10
Purchase #4	$28.27	3.451%	$29.2456	$29.25	$29.25	$29.20
Purchase #5	$59.43	13.168%	$67.2557	$67.26	$67.25	$67.30
Purchase #6	$63.94	13.314%	$72.453	$72.45	$72.45	$72.50
Purchase #7	$129.87	11.832%	$145.2362	$145.24	$145.25	$145.20
7 purchase totals =	$539.49		$604.9327	$604.94	$604.90	$604.90