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	$79.78	12.648%	$89.8706	$89.87	$89.85	$89.90
Purchase #2	$38.87	8.302%	$42.097	$42.10	$42.10	$42.10
Purchase #3	$237.94	11.688%	$265.7504	$265.75	$265.75	$265.80
Purchase #4	$28.67	12.824%	$32.3466	$32.35	$32.35	$32.30
Purchase #5	$185.28	8.367%	$200.7824	$200.78	$200.80	$200.80
Purchase #6	$135.94	5.479%	$143.3882	$143.39	$143.40	$143.40
Purchase #7	$44.80	4.242%	$46.7004	$46.70	$46.70	$46.70
7 purchase totals =	$751.28		$820.9356	$820.94	$820.95	$821.00