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	$70.32	9.828%	$77.231	$77.23	$77.25	$77.20
Purchase #2	$78.40	11.508%	$87.4223	$87.42	$87.40	$87.40
Purchase #3	$245.71	10.673%	$271.9346	$271.93	$271.95	$271.90
Purchase #4	$37.95	10.144%	$41.7996	$41.80	$41.80	$41.80
Purchase #5	$179.46	4.525%	$187.5806	$187.58	$187.60	$187.60
Purchase #6	$92.80	13.604%	$105.4245	$105.42	$105.40	$105.40
Purchase #7	$161.40	4.243%	$168.2482	$168.25	$168.25	$168.20
7 purchase totals =	$866.04		$939.6408	$939.63	$939.65	$939.50