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	$80.56	6.153%	$85.5169	$85.52	$85.50	$85.50
Purchase #2	$38.75	10.780%	$42.9273	$42.93	$42.95	$42.90
Purchase #3	$55.40	13.200%	$62.7128	$62.71	$62.70	$62.70
Purchase #4	$237.67	8.739%	$258.44	$258.44	$258.45	$258.40
Purchase #5	$168.33	3.339%	$173.9505	$173.95	$173.95	$174.00
Purchase #6	$158.93	7.851%	$171.4076	$171.41	$171.40	$171.40
Purchase #7	$195.84	12.637%	$220.5883	$220.59	$220.60	$220.60
7 purchase totals =	$935.48		$1,015.5434	$1,015.55	$1,015.55	$1,015.50