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	$88.81	13.620%	$100.9059	$100.91	$100.90	$100.90
Purchase #2	$10.96	11.478%	$12.218	$12.22	$12.20	$12.20
Purchase #3	$37.37	12.109%	$41.8951	$41.90	$41.90	$41.90
Purchase #4	$212.91	6.822%	$227.4347	$227.43	$227.45	$227.40
Purchase #5	$166.55	13.158%	$188.4646	$188.46	$188.45	$188.50
Purchase #6	$242.78	5.816%	$256.9001	$256.90	$256.90	$256.90
Purchase #7	$55.99	12.867%	$63.1942	$63.19	$63.20	$63.20
7 purchase totals =	$815.37		$891.0126	$891.01	$891.00	$891.00