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	$26.68	12.119%	$29.9133	$29.91	$29.90	$29.90
Purchase #2	$112.42	12.790%	$126.7985	$126.80	$126.80	$126.80
Purchase #3	$37.73	12.446%	$42.4259	$42.43	$42.45	$42.40
Purchase #4	$52.53	6.297%	$55.8378	$55.84	$55.85	$55.80
Purchase #5	$52.41	4.382%	$54.7066	$54.71	$54.70	$54.70
Purchase #6	$178.81	4.250%	$186.4094	$186.41	$186.40	$186.40
Purchase #7	$85.50	11.178%	$95.0572	$95.06	$95.05	$95.10
7 purchase totals =	$546.08		$591.1487	$591.16	$591.15	$591.10