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	$74.73	7.173%	$80.0904	$80.09	$80.10	$80.10
Purchase #2	$179.28	3.255%	$185.1156	$185.12	$185.10	$185.10
Purchase #3	$22.43	8.189%	$24.2668	$24.27	$24.25	$24.30
Purchase #4	$37.25	7.829%	$40.1663	$40.17	$40.15	$40.20
Purchase #5	$104.45	9.247%	$114.1085	$114.11	$114.10	$114.10
Purchase #6	$42.53	7.117%	$45.5569	$45.56	$45.55	$45.60
Purchase #7	$82.60	9.120%	$90.1331	$90.13	$90.15	$90.10
7 purchase totals =	$543.27		$579.4376	$579.45	$579.40	$579.50