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	$90.92	13.845%	$103.5079	$103.51	$103.50	$103.50
Purchase #2	$92.51	6.564%	$98.5824	$98.58	$98.60	$98.60
Purchase #3	$234.41	10.385%	$258.7535	$258.75	$258.75	$258.80
Purchase #4	$69.40	12.582%	$78.1319	$78.13	$78.15	$78.10
Purchase #5	$98.63	3.802%	$102.3799	$102.38	$102.40	$102.40
Purchase #6	$172.35	7.783%	$185.764	$185.76	$185.75	$185.80
Purchase #7	$38.38	3.561%	$39.7467	$39.75	$39.75	$39.70
7 purchase totals =	$796.60		$866.8663	$866.86	$866.90	$866.90