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	$35.34	7.114%	$37.8541	$37.85	$37.85	$37.90
Purchase #2	$234.78	13.773%	$267.1162	$267.12	$267.10	$267.10
Purchase #3	$45.49	9.714%	$49.9089	$49.91	$49.90	$49.90
Purchase #4	$61.74	7.586%	$66.4236	$66.42	$66.40	$66.40
Purchase #5	$105.38	7.567%	$113.3541	$113.35	$113.35	$113.40
Purchase #6	$32.74	5.457%	$34.5266	$34.53	$34.55	$34.50
Purchase #7	$231.33	10.432%	$255.4623	$255.46	$255.45	$255.50
7 purchase totals =	$746.80		$824.6458	$824.64	$824.60	$824.70