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	$117.72	12.225%	$132.1113	$132.11	$132.10	$132.10
Purchase #2	$121.30	10.596%	$134.1529	$134.15	$134.15	$134.20
Purchase #3	$85.91	3.358%	$88.7949	$88.79	$88.80	$88.80
Purchase #4	$42.55	13.546%	$48.3138	$48.31	$48.30	$48.30
Purchase #5	$213.28	11.660%	$238.1484	$238.15	$238.15	$238.10
Purchase #6	$41.36	4.746%	$43.3229	$43.32	$43.30	$43.30
Purchase #7	$18.29	7.111%	$19.5906	$19.59	$19.60	$19.60
7 purchase totals =	$640.41		$704.4348	$704.42	$704.40	$704.40