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	$67.55	12.295%	$75.8553	$75.86	$75.85	$75.90
Purchase #2	$161.56	10.720%	$178.8792	$178.88	$178.90	$178.90
Purchase #3	$109.52	13.546%	$124.3556	$124.36	$124.35	$124.40
Purchase #4	$214.54	6.162%	$227.76	$227.76	$227.75	$227.80
Purchase #5	$37.82	4.228%	$39.419	$39.42	$39.40	$39.40
Purchase #6	$25.87	5.586%	$27.3151	$27.32	$27.30	$27.30
Purchase #7	$29.46	9.479%	$32.2525	$32.25	$32.25	$32.30
7 purchase totals =	$646.32		$705.8367	$705.85	$705.80	$706.00