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	$91.81	13.141%	$103.8748	$103.87	$103.85	$103.90
Purchase #2	$191.35	9.550%	$209.6239	$209.62	$209.60	$209.60
Purchase #3	$18.40	6.476%	$19.5916	$19.59	$19.60	$19.60
Purchase #4	$62.95	4.745%	$65.937	$65.94	$65.95	$65.90
Purchase #5	$38.48	7.506%	$41.3683	$41.37	$41.35	$41.40
Purchase #6	$152.62	13.704%	$173.535	$173.54	$173.55	$173.50
Purchase #7	$43.92	6.601%	$46.8192	$46.82	$46.80	$46.80
7 purchase totals =	$599.53		$660.7498	$660.75	$660.70	$660.70