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	$158.82	9.138%	$173.333	$173.33	$173.35	$173.30
Purchase #2	$137.27	4.118%	$142.9228	$142.92	$142.90	$142.90
Purchase #3	$20.41	6.357%	$21.7075	$21.71	$21.70	$21.70
Purchase #4	$33.52	12.250%	$37.6262	$37.63	$37.65	$37.60
Purchase #5	$34.33	6.415%	$36.5323	$36.53	$36.55	$36.50
Purchase #6	$46.47	7.481%	$49.9464	$49.95	$49.95	$49.90
Purchase #7	$28.79	12.835%	$32.4852	$32.49	$32.50	$32.50
7 purchase totals =	$459.61		$494.5534	$494.56	$494.60	$494.40