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	$245.83	6.616%	$262.0941	$262.09	$262.10	$262.10
Purchase #2	$172.57	13.383%	$195.665	$195.67	$195.65	$195.70
Purchase #3	$5.81	13.699%	$6.6059	$6.61	$6.60	$6.60
Purchase #4	$77.31	5.205%	$81.334	$81.33	$81.35	$81.30
Purchase #5	$64.86	10.583%	$71.7241	$71.72	$71.70	$71.70
Purchase #6	$42.41	7.120%	$45.4296	$45.43	$45.45	$45.40
Purchase #7	$5.99	11.644%	$6.6875	$6.69	$6.70	$6.70
7 purchase totals =	$614.78		$669.5402	$669.54	$669.55	$669.50