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	$166.33	11.599%	$185.6226	$185.62	$185.60	$185.60
Purchase #2	$133.72	9.438%	$146.3405	$146.34	$146.35	$146.30
Purchase #3	$223.68	6.226%	$237.6063	$237.61	$237.60	$237.60
Purchase #4	$180.37	5.741%	$190.725	$190.73	$190.75	$190.70
Purchase #5	$114.81	4.272%	$119.7147	$119.71	$119.70	$119.70
Purchase #6	$228.32	6.238%	$242.5626	$242.56	$242.55	$242.60
Purchase #7	$134.64	13.651%	$153.0197	$153.02	$153.00	$153.00
7 purchase totals =	$1,181.87		$1,275.5914	$1,275.59	$1,275.55	$1,275.50