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	$39.94	5.452%	$42.1175	$42.12	$42.10	$42.10
Purchase #2	$227.77	9.419%	$249.2237	$249.22	$249.20	$249.20
Purchase #3	$157.81	6.377%	$167.8735	$167.87	$167.85	$167.90
Purchase #4	$222.42	4.784%	$233.0606	$233.06	$233.05	$233.10
Purchase #5	$53.97	8.266%	$58.4312	$58.43	$58.45	$58.40
Purchase #6	$172.37	10.499%	$190.4671	$190.47	$190.45	$190.50
Purchase #7	$27.34	3.565%	$28.3147	$28.31	$28.30	$28.30
7 purchase totals =	$901.62		$969.4883	$969.48	$969.40	$969.50