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	$160.50	3.183%	$165.6087	$165.61	$165.60	$165.60
Purchase #2	$192.40	10.410%	$212.4288	$212.43	$212.45	$212.40
Purchase #3	$72.78	10.106%	$80.1351	$80.14	$80.15	$80.10
Purchase #4	$163.27	3.783%	$169.4465	$169.45	$169.45	$169.40
Purchase #5	$127.59	3.617%	$132.2049	$132.20	$132.20	$132.20
Purchase #6	$51.40	3.459%	$53.1779	$53.18	$53.20	$53.20
Purchase #7	$17.43	6.181%	$18.5073	$18.51	$18.50	$18.50
7 purchase totals =	$785.37		$831.5092	$831.52	$831.55	$831.40