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	$199.38	11.593%	$222.4941	$222.49	$222.50	$222.50
Purchase #2	$58.75	13.352%	$66.5943	$66.59	$66.60	$66.60
Purchase #3	$193.41	12.488%	$217.563	$217.56	$217.55	$217.60
Purchase #4	$208.47	13.686%	$237.0012	$237.00	$237.00	$237.00
Purchase #5	$151.58	13.567%	$172.1449	$172.14	$172.15	$172.10
Purchase #6	$98.61	5.693%	$104.2239	$104.22	$104.20	$104.20
Purchase #7	$65.96	6.590%	$70.3068	$70.31	$70.30	$70.30
7 purchase totals =	$976.16		$1,090.3282	$1,090.31	$1,090.30	$1,090.30