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	$151.40	9.102%	$165.1804	$165.18	$165.20	$165.20
Purchase #2	$39.60	9.683%	$43.4345	$43.43	$43.45	$43.40
Purchase #3	$196.85	11.826%	$220.1295	$220.13	$220.15	$220.10
Purchase #4	$201.61	3.620%	$208.9083	$208.91	$208.90	$208.90
Purchase #5	$128.79	7.274%	$138.1582	$138.16	$138.15	$138.20
Purchase #6	$239.75	4.452%	$250.4237	$250.42	$250.40	$250.40
Purchase #7	$184.86	3.770%	$191.8292	$191.83	$191.85	$191.80
7 purchase totals =	$1,142.86		$1,218.0638	$1,218.06	$1,218.10	$1,218.00