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	$115.49	4.429%	$120.6051	$120.61	$120.60	$120.60
Purchase #2	$201.73	10.119%	$222.1431	$222.14	$222.15	$222.10
Purchase #3	$176.42	4.581%	$184.5018	$184.50	$184.50	$184.50
Purchase #4	$43.99	3.625%	$45.5846	$45.58	$45.60	$45.60
Purchase #5	$49.95	9.563%	$54.7267	$54.73	$54.75	$54.70
Purchase #6	$119.93	7.452%	$128.8672	$128.87	$128.85	$128.90
Purchase #7	$149.82	11.365%	$166.847	$166.85	$166.85	$166.80
7 purchase totals =	$857.33		$923.2755	$923.28	$923.30	$923.20