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	$12.89	6.271%	$13.6983	$13.70	$13.70	$13.70
Purchase #2	$227.35	10.380%	$250.9489	$250.95	$250.95	$250.90
Purchase #3	$98.29	6.156%	$104.3407	$104.34	$104.35	$104.30
Purchase #4	$204.74	11.720%	$228.7355	$228.74	$228.75	$228.70
Purchase #5	$185.59	10.800%	$205.6337	$205.63	$205.65	$205.60
Purchase #6	$52.39	6.867%	$55.9876	$55.99	$56.00	$56.00
Purchase #7	$202.76	9.721%	$222.4703	$222.47	$222.45	$222.50
7 purchase totals =	$984.01		$1,081.8150	$1,081.82	$1,081.85	$1,081.70