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	$26.47	6.866%	$28.2874	$28.29	$28.30	$28.30
Purchase #2	$136.42	10.182%	$150.3103	$150.31	$150.30	$150.30
Purchase #3	$171.98	10.481%	$190.0052	$190.01	$190.00	$190.00
Purchase #4	$58.66	13.473%	$66.5633	$66.56	$66.55	$66.60
Purchase #5	$103.71	6.321%	$110.2655	$110.27	$110.25	$110.30
Purchase #6	$34.71	13.482%	$39.3896	$39.39	$39.40	$39.40
Purchase #7	$215.52	5.470%	$227.3089	$227.31	$227.30	$227.30
7 purchase totals =	$747.47		$812.1302	$812.14	$812.10	$812.20