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	$29.29	8.710%	$31.8412	$31.84	$31.85	$31.80
Purchase #2	$62.45	12.581%	$70.3068	$70.31	$70.30	$70.30
Purchase #3	$66.88	10.244%	$73.7312	$73.73	$73.75	$73.70
Purchase #4	$206.88	8.253%	$223.9538	$223.95	$223.95	$224.00
Purchase #5	$25.54	9.716%	$28.0215	$28.02	$28.00	$28.00
Purchase #6	$235.86	8.153%	$255.0897	$255.09	$255.10	$255.10
Purchase #7	$131.98	7.130%	$141.3902	$141.39	$141.40	$141.40
7 purchase totals =	$758.88		$824.3344	$824.33	$824.35	$824.30