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	$112.40	13.341%	$127.3953	$127.40	$127.40	$127.40
Purchase #2	$157.69	5.218%	$165.9183	$165.92	$165.90	$165.90
Purchase #3	$98.41	11.217%	$109.4486	$109.45	$109.45	$109.40
Purchase #4	$35.98	6.358%	$38.2676	$38.27	$38.25	$38.30
Purchase #5	$39.32	9.249%	$42.9567	$42.96	$42.95	$43.00
Purchase #6	$98.74	12.662%	$111.2425	$111.24	$111.25	$111.20
Purchase #7	$111.79	8.771%	$121.5951	$121.60	$121.60	$121.60
7 purchase totals =	$654.33		$716.8241	$716.84	$716.80	$716.80