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	$172.59	3.307%	$178.2976	$178.30	$178.30	$178.30
Purchase #2	$98.91	10.425%	$109.2214	$109.22	$109.20	$109.20
Purchase #3	$128.98	12.635%	$145.2766	$145.28	$145.30	$145.30
Purchase #4	$69.56	3.795%	$72.1998	$72.20	$72.20	$72.20
Purchase #5	$64.96	12.793%	$73.2703	$73.27	$73.25	$73.30
Purchase #6	$68.29	13.498%	$77.5078	$77.51	$77.50	$77.50
Purchase #7	$142.50	10.600%	$157.605	$157.61	$157.60	$157.60
7 purchase totals =	$745.79		$813.3785	$813.39	$813.35	$813.40