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	$165.52	7.607%	$178.1111	$178.11	$178.10	$178.10
Purchase #2	$133.71	3.570%	$138.4834	$138.48	$138.50	$138.50
Purchase #3	$115.66	13.746%	$131.5586	$131.56	$131.55	$131.60
Purchase #4	$20.91	11.748%	$23.3665	$23.37	$23.35	$23.40
Purchase #5	$123.39	13.767%	$140.3771	$140.38	$140.40	$140.40
Purchase #6	$61.48	10.449%	$67.904	$67.90	$67.90	$67.90
Purchase #7	$90.71	13.325%	$102.7971	$102.80	$102.80	$102.80
7 purchase totals =	$711.38		$782.5978	$782.60	$782.60	$782.70