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	$51.94	5.300%	$54.6928	$54.69	$54.70	$54.70
Purchase #2	$173.50	8.666%	$188.5355	$188.54	$188.55	$188.50
Purchase #3	$242.25	7.468%	$260.3412	$260.34	$260.35	$260.30
Purchase #4	$204.86	13.365%	$232.2395	$232.24	$232.25	$232.20
Purchase #5	$179.89	11.543%	$200.6547	$200.65	$200.65	$200.70
Purchase #6	$213.73	11.176%	$237.6165	$237.62	$237.60	$237.60
Purchase #7	$38.72	10.360%	$42.7314	$42.73	$42.75	$42.70
7 purchase totals =	$1,104.89		$1,216.8116	$1,216.81	$1,216.85	$1,216.70