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	$85.33	12.403%	$95.9135	$95.91	$95.90	$95.90
Purchase #2	$121.50	5.256%	$127.886	$127.89	$127.90	$127.90
Purchase #3	$24.45	8.720%	$26.582	$26.58	$26.60	$26.60
Purchase #4	$123.80	13.537%	$140.5588	$140.56	$140.55	$140.60
Purchase #5	$167.34	4.263%	$174.4737	$174.47	$174.45	$174.50
Purchase #6	$18.53	3.602%	$19.1975	$19.20	$19.20	$19.20
Purchase #7	$83.59	7.828%	$90.1334	$90.13	$90.15	$90.10
7 purchase totals =	$624.54		$674.7449	$674.74	$674.75	$674.80