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	$99.72	12.826%	$112.5101	$112.51	$112.50	$112.50
Purchase #2	$52.37	8.205%	$56.667	$56.67	$56.65	$56.70
Purchase #3	$155.25	8.656%	$168.6884	$168.69	$168.70	$168.70
Purchase #4	$74.42	5.202%	$78.2913	$78.29	$78.30	$78.30
Purchase #5	$66.72	6.848%	$71.289	$71.29	$71.30	$71.30
Purchase #6	$68.83	10.712%	$76.2031	$76.20	$76.20	$76.20
Purchase #7	$203.54	7.274%	$218.3455	$218.35	$218.35	$218.30
7 purchase totals =	$720.85		$781.9944	$782.00	$782.00	$782.00