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	$53.97	12.674%	$60.8102	$60.81	$60.80	$60.80
Purchase #2	$106.48	5.550%	$112.3896	$112.39	$112.40	$112.40
Purchase #3	$32.38	9.265%	$35.38	$35.38	$35.40	$35.40
Purchase #4	$199.72	10.427%	$220.5448	$220.54	$220.55	$220.50
Purchase #5	$26.39	4.697%	$27.6295	$27.63	$27.65	$27.60
Purchase #6	$90.37	13.591%	$102.6522	$102.65	$102.65	$102.70
Purchase #7	$84.43	7.638%	$90.8788	$90.88	$90.90	$90.90
7 purchase totals =	$593.74		$650.2851	$650.28	$650.35	$650.30