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	$87.95	13.424%	$99.7564	$99.76	$99.75	$99.80
Purchase #2	$108.69	13.830%	$123.7218	$123.72	$123.70	$123.70
Purchase #3	$56.26	4.734%	$58.9233	$58.92	$58.90	$58.90
Purchase #4	$243.38	5.776%	$257.4376	$257.44	$257.45	$257.40
Purchase #5	$22.54	7.606%	$24.2544	$24.25	$24.25	$24.30
Purchase #6	$114.64	8.121%	$123.9499	$123.95	$123.95	$123.90
Purchase #7	$181.85	4.233%	$189.5477	$189.55	$189.55	$189.50
7 purchase totals =	$815.31		$877.5911	$877.59	$877.55	$877.50