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	$134.59	10.482%	$148.6977	$148.70	$148.70	$148.70
Purchase #2	$205.73	3.139%	$212.1879	$212.19	$212.20	$212.20
Purchase #3	$72.74	10.792%	$80.5901	$80.59	$80.60	$80.60
Purchase #4	$37.93	8.328%	$41.0888	$41.09	$41.10	$41.10
Purchase #5	$40.95	4.308%	$42.7141	$42.71	$42.70	$42.70
Purchase #6	$160.38	12.524%	$180.466	$180.47	$180.45	$180.50
Purchase #7	$67.64	4.360%	$70.5891	$70.59	$70.60	$70.60
7 purchase totals =	$719.96		$776.3337	$776.34	$776.35	$776.40