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	$240.55	6.395%	$255.9332	$255.93	$255.95	$255.90
Purchase #2	$226.74	4.254%	$236.3855	$236.39	$236.40	$236.40
Purchase #3	$183.32	5.801%	$193.9544	$193.95	$193.95	$194.00
Purchase #4	$200.25	11.538%	$223.3548	$223.35	$223.35	$223.40
Purchase #5	$227.83	12.144%	$255.4977	$255.50	$255.50	$255.50
Purchase #6	$98.71	8.353%	$106.9552	$106.96	$106.95	$107.00
Purchase #7	$53.86	11.204%	$59.8945	$59.89	$59.90	$59.90
7 purchase totals =	$1,231.26		$1,331.9753	$1,331.97	$1,332.00	$1,332.10