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	$70.85	10.647%	$78.3934	$78.39	$78.40	$78.40
Purchase #2	$234.36	5.530%	$247.3201	$247.32	$247.30	$247.30
Purchase #3	$61.48	5.178%	$64.6634	$64.66	$64.65	$64.70
Purchase #4	$18.57	13.517%	$21.0801	$21.08	$21.10	$21.10
Purchase #5	$144.91	5.381%	$152.7076	$152.71	$152.70	$152.70
Purchase #6	$56.65	5.788%	$59.9289	$59.93	$59.95	$59.90
Purchase #7	$53.45	6.611%	$56.9836	$56.98	$57.00	$57.00
7 purchase totals =	$640.27		$681.0771	$681.07	$681.10	$681.10