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	$85.95	4.767%	$90.0472	$90.05	$90.05	$90.00
Purchase #2	$138.69	4.416%	$144.8146	$144.81	$144.80	$144.80
Purchase #3	$213.71	10.765%	$236.7159	$236.72	$236.70	$236.70
Purchase #4	$60.37	4.164%	$62.8838	$62.88	$62.90	$62.90
Purchase #5	$192.68	12.362%	$216.4991	$216.50	$216.50	$216.50
Purchase #6	$29.52	13.188%	$33.4131	$33.41	$33.40	$33.40
Purchase #7	$20.28	3.242%	$20.9375	$20.94	$20.95	$20.90
7 purchase totals =	$741.20		$805.3112	$805.31	$805.30	$805.20