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	$60.44	5.255%	$63.6161	$63.62	$63.60	$63.60
Purchase #2	$99.50	4.433%	$103.9108	$103.91	$103.90	$103.90
Purchase #3	$37.26	13.277%	$42.207	$42.21	$42.20	$42.20
Purchase #4	$231.33	10.871%	$256.4779	$256.48	$256.50	$256.50
Purchase #5	$104.85	4.529%	$109.5987	$109.60	$109.60	$109.60
Purchase #6	$115.58	5.455%	$121.8849	$121.88	$121.90	$121.90
Purchase #7	$127.95	12.404%	$143.8209	$143.82	$143.80	$143.80
7 purchase totals =	$776.91		$841.5163	$841.52	$841.50	$841.50