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	$130.95	10.434%	$144.6133	$144.61	$144.60	$144.60
Purchase #2	$150.68	6.244%	$160.0885	$160.09	$160.10	$160.10
Purchase #3	$196.53	10.807%	$217.769	$217.77	$217.75	$217.80
Purchase #4	$193.74	8.291%	$209.803	$209.80	$209.80	$209.80
Purchase #5	$28.91	5.630%	$30.5376	$30.54	$30.55	$30.50
Purchase #6	$195.77	13.718%	$222.6257	$222.63	$222.65	$222.60
Purchase #7	$104.49	9.673%	$114.5973	$114.60	$114.60	$114.60
7 purchase totals =	$1,001.07		$1,100.0344	$1,100.04	$1,100.05	$1,100.00