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	$151.25	6.592%	$161.2204	$161.22	$161.20	$161.20
Purchase #2	$30.31	13.725%	$34.47	$34.47	$34.45	$34.50
Purchase #3	$161.94	3.447%	$167.5221	$167.52	$167.50	$167.50
Purchase #4	$75.94	12.361%	$85.3269	$85.33	$85.35	$85.30
Purchase #5	$123.74	8.336%	$134.055	$134.06	$134.05	$134.10
Purchase #6	$84.43	7.282%	$90.5782	$90.58	$90.60	$90.60
Purchase #7	$128.34	10.208%	$141.4409	$141.44	$141.45	$141.40
7 purchase totals =	$755.95		$814.6135	$814.62	$814.60	$814.60