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	$121.79	13.153%	$137.809	$137.81	$137.80	$137.80
Purchase #2	$18.77	12.299%	$21.0785	$21.08	$21.10	$21.10
Purchase #3	$46.51	13.549%	$52.8116	$52.81	$52.80	$52.80
Purchase #4	$137.31	13.336%	$155.6217	$155.62	$155.60	$155.60
Purchase #5	$167.68	10.681%	$185.5899	$185.59	$185.60	$185.60
Purchase #6	$37.67	12.316%	$42.3094	$42.31	$42.30	$42.30
Purchase #7	$26.74	8.416%	$28.9904	$28.99	$29.00	$29.00
7 purchase totals =	$556.47		$624.2105	$624.21	$624.20	$624.20