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	$53.63	3.602%	$55.5618	$55.56	$55.55	$55.60
Purchase #2	$63.77	11.725%	$71.247	$71.25	$71.25	$71.20
Purchase #3	$52.75	5.119%	$55.4503	$55.45	$55.45	$55.50
Purchase #4	$173.28	6.682%	$184.8586	$184.86	$184.85	$184.90
Purchase #5	$222.59	8.822%	$242.2269	$242.23	$242.25	$242.20
Purchase #6	$241.48	8.248%	$261.3973	$261.40	$261.40	$261.40
Purchase #7	$92.71	7.452%	$99.6187	$99.62	$99.60	$99.60
7 purchase totals =	$900.21		$970.3606	$970.37	$970.35	$970.40