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	$28.35	4.165%	$29.5308	$29.53	$29.55	$29.50
Purchase #2	$161.49	7.189%	$173.0995	$173.10	$173.10	$173.10
Purchase #3	$120.69	11.106%	$134.0938	$134.09	$134.10	$134.10
Purchase #4	$160.53	4.160%	$167.208	$167.21	$167.20	$167.20
Purchase #5	$99.56	4.551%	$104.091	$104.09	$104.10	$104.10
Purchase #6	$155.27	8.515%	$168.4912	$168.49	$168.50	$168.50
Purchase #7	$226.72	12.648%	$255.3955	$255.40	$255.40	$255.40
7 purchase totals =	$952.61		$1,031.9098	$1,031.91	$1,031.95	$1,031.90