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	$45.56	9.692%	$49.9757	$49.98	$50.00	$50.00
Purchase #2	$88.26	9.484%	$96.6306	$96.63	$96.65	$96.60
Purchase #3	$153.53	4.406%	$160.2945	$160.29	$160.30	$160.30
Purchase #4	$225.75	10.653%	$249.7991	$249.80	$249.80	$249.80
Purchase #5	$200.33	13.658%	$227.6911	$227.69	$227.70	$227.70
Purchase #6	$235.48	10.176%	$259.4424	$259.44	$259.45	$259.40
Purchase #7	$104.59	6.818%	$111.7209	$111.72	$111.70	$111.70
7 purchase totals =	$1,053.50		$1,155.5543	$1,155.55	$1,155.60	$1,155.50