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	$149.31	10.315%	$164.7113	$164.71	$164.70	$164.70
Purchase #2	$216.67	11.332%	$241.223	$241.22	$241.20	$241.20
Purchase #3	$90.96	10.180%	$100.2197	$100.22	$100.20	$100.20
Purchase #4	$232.76	4.223%	$242.5895	$242.59	$242.60	$242.60
Purchase #5	$104.87	3.358%	$108.3915	$108.39	$108.40	$108.40
Purchase #6	$5.42	9.150%	$5.9159	$5.92	$5.90	$5.90
Purchase #7	$180.27	6.608%	$192.1822	$192.18	$192.20	$192.20
7 purchase totals =	$980.26		$1,055.2331	$1,055.23	$1,055.20	$1,055.20