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	$167.49	6.380%	$178.1759	$178.18	$178.20	$178.20
Purchase #2	$47.42	6.277%	$50.3966	$50.40	$50.40	$50.40
Purchase #3	$191.76	4.520%	$200.4276	$200.43	$200.45	$200.40
Purchase #4	$87.32	12.828%	$98.5214	$98.52	$98.50	$98.50
Purchase #5	$131.32	10.571%	$145.2018	$145.20	$145.20	$145.20
Purchase #6	$168.38	3.603%	$174.4467	$174.45	$174.45	$174.40
Purchase #7	$128.27	13.510%	$145.5993	$145.60	$145.60	$145.60
7 purchase totals =	$921.96		$992.7693	$992.78	$992.80	$992.70