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	$29.38	10.686%	$32.5195	$32.52	$32.50	$32.50
Purchase #2	$6.58	7.328%	$7.0622	$7.06	$7.05	$7.10
Purchase #3	$89.76	9.508%	$98.2944	$98.29	$98.30	$98.30
Purchase #4	$65.81	3.702%	$68.2463	$68.25	$68.25	$68.20
Purchase #5	$73.81	6.318%	$78.4733	$78.47	$78.45	$78.50
Purchase #6	$38.77	5.652%	$40.9613	$40.96	$40.95	$41.00
Purchase #7	$149.73	10.439%	$165.3603	$165.36	$165.35	$165.40
7 purchase totals =	$453.84		$490.9173	$490.91	$490.85	$491.00