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	$245.74	4.119%	$255.862	$255.86	$255.85	$255.90
Purchase #2	$135.66	8.752%	$147.533	$147.53	$147.55	$147.50
Purchase #3	$30.94	12.417%	$34.7818	$34.78	$34.80	$34.80
Purchase #4	$196.40	4.821%	$205.8684	$205.87	$205.85	$205.90
Purchase #5	$55.43	6.139%	$58.8328	$58.83	$58.85	$58.80
Purchase #6	$85.89	6.598%	$91.557	$91.56	$91.55	$91.60
Purchase #7	$24.80	13.253%	$28.0867	$28.09	$28.10	$28.10
7 purchase totals =	$774.86		$822.5217	$822.52	$822.55	$822.60