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	$143.41	6.872%	$153.2651	$153.27	$153.25	$153.30
Purchase #2	$205.98	6.124%	$218.5942	$218.59	$218.60	$218.60
Purchase #3	$16.93	9.220%	$18.4909	$18.49	$18.50	$18.50
Purchase #4	$11.33	7.812%	$12.2151	$12.22	$12.20	$12.20
Purchase #5	$157.75	9.264%	$172.364	$172.36	$172.35	$172.40
Purchase #6	$134.68	13.655%	$153.0706	$153.07	$153.05	$153.10
Purchase #7	$55.26	10.176%	$60.8833	$60.88	$60.90	$60.90
7 purchase totals =	$725.34		$788.8832	$788.88	$788.85	$789.00