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	$140.40	11.304%	$156.2708	$156.27	$156.25	$156.30
Purchase #2	$90.57	13.851%	$103.1149	$103.11	$103.10	$103.10
Purchase #3	$127.99	10.822%	$141.8411	$141.84	$141.85	$141.80
Purchase #4	$177.85	5.599%	$187.8078	$187.81	$187.80	$187.80
Purchase #5	$224.44	8.198%	$242.8396	$242.84	$242.85	$242.80
Purchase #6	$38.58	9.568%	$42.2713	$42.27	$42.25	$42.30
Purchase #7	$72.95	11.838%	$81.5858	$81.59	$81.60	$81.60
7 purchase totals =	$872.78		$955.7313	$955.73	$955.70	$955.70