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	$209.39	12.125%	$234.7785	$234.78	$234.80	$234.80
Purchase #2	$42.50	7.131%	$45.5307	$45.53	$45.55	$45.50
Purchase #3	$33.34	7.557%	$35.8595	$35.86	$35.85	$35.90
Purchase #4	$127.60	11.670%	$142.4909	$142.49	$142.50	$142.50
Purchase #5	$58.26	7.408%	$62.5759	$62.58	$62.60	$62.60
Purchase #6	$137.62	6.769%	$146.9355	$146.94	$146.95	$146.90
Purchase #7	$163.61	5.231%	$172.1684	$172.17	$172.15	$172.20
7 purchase totals =	$772.32		$840.3394	$840.35	$840.40	$840.40