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	$155.28	7.170%	$166.4136	$166.41	$166.40	$166.40
Purchase #2	$59.26	11.620%	$66.146	$66.15	$66.15	$66.10
Purchase #3	$221.36	8.659%	$240.5276	$240.53	$240.55	$240.50
Purchase #4	$50.94	13.245%	$57.687	$57.69	$57.70	$57.70
Purchase #5	$158.91	13.649%	$180.5996	$180.60	$180.60	$180.60
Purchase #6	$162.94	9.571%	$178.535	$178.54	$178.55	$178.50
Purchase #7	$29.90	13.139%	$33.8286	$33.83	$33.85	$33.80
7 purchase totals =	$838.59		$923.7374	$923.75	$923.80	$923.60