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	$33.57	11.485%	$37.4255	$37.43	$37.45	$37.40
Purchase #2	$193.62	13.545%	$219.8458	$219.85	$219.85	$219.80
Purchase #3	$128.98	11.484%	$143.7921	$143.79	$143.80	$143.80
Purchase #4	$153.60	10.544%	$169.7956	$169.80	$169.80	$169.80
Purchase #5	$71.65	12.637%	$80.7044	$80.70	$80.70	$80.70
Purchase #6	$49.85	9.222%	$54.4472	$54.45	$54.45	$54.40
Purchase #7	$74.79	11.608%	$83.4716	$83.47	$83.45	$83.50
7 purchase totals =	$706.06		$789.4822	$789.49	$789.50	$789.40