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	$137.74	3.563%	$142.6477	$142.65	$142.65	$142.60
Purchase #2	$158.79	6.184%	$168.6096	$168.61	$168.60	$168.60
Purchase #3	$169.31	12.491%	$190.4585	$190.46	$190.45	$190.50
Purchase #4	$97.43	12.631%	$109.7364	$109.74	$109.75	$109.70
Purchase #5	$240.65	3.564%	$249.2268	$249.23	$249.25	$249.20
Purchase #6	$16.61	9.329%	$18.1595	$18.16	$18.15	$18.20
Purchase #7	$173.71	12.605%	$195.6061	$195.61	$195.60	$195.60
7 purchase totals =	$994.24		$1,074.4446	$1,074.46	$1,074.45	$1,074.40