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	$45.42	7.843%	$48.9823	$48.98	$49.00	$49.00
Purchase #2	$103.67	7.836%	$111.7936	$111.79	$111.80	$111.80
Purchase #3	$188.47	6.181%	$200.1193	$200.12	$200.10	$200.10
Purchase #4	$54.30	9.219%	$59.3059	$59.31	$59.30	$59.30
Purchase #5	$246.70	5.143%	$259.3878	$259.39	$259.40	$259.40
Purchase #6	$236.76	6.262%	$251.5859	$251.59	$251.60	$251.60
Purchase #7	$16.93	13.231%	$19.17	$19.17	$19.15	$19.20
7 purchase totals =	$892.25		$950.3448	$950.35	$950.35	$950.40