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	$168.85	6.141%	$179.2191	$179.22	$179.20	$179.20
Purchase #2	$17.76	13.405%	$20.1407	$20.14	$20.15	$20.10
Purchase #3	$200.63	12.434%	$225.5763	$225.58	$225.60	$225.60
Purchase #4	$128.42	8.616%	$139.4847	$139.48	$139.50	$139.50
Purchase #5	$58.88	8.196%	$63.7058	$63.71	$63.70	$63.70
Purchase #6	$131.65	8.331%	$142.6178	$142.62	$142.60	$142.60
Purchase #7	$120.60	6.413%	$128.3341	$128.33	$128.35	$128.30
7 purchase totals =	$826.79		$899.0785	$899.08	$899.10	$899.00