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	$111.61	10.384%	$123.1996	$123.20	$123.20	$123.20
Purchase #2	$79.42	13.623%	$90.2394	$90.24	$90.25	$90.20
Purchase #3	$189.92	4.470%	$198.4094	$198.41	$198.40	$198.40
Purchase #4	$106.38	11.430%	$118.5392	$118.54	$118.55	$118.50
Purchase #5	$229.47	9.212%	$250.6088	$250.61	$250.60	$250.60
Purchase #6	$166.39	3.847%	$172.791	$172.79	$172.80	$172.80
Purchase #7	$197.65	7.756%	$212.9797	$212.98	$213.00	$213.00
7 purchase totals =	$1,080.84		$1,166.7671	$1,166.77	$1,166.80	$1,166.70