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	$20.55	12.149%	$23.0466	$23.05	$23.05	$23.00
Purchase #2	$69.56	10.280%	$76.7108	$76.71	$76.70	$76.70
Purchase #3	$151.51	4.465%	$158.2749	$158.27	$158.25	$158.30
Purchase #4	$44.89	5.345%	$47.2894	$47.29	$47.30	$47.30
Purchase #5	$140.79	7.175%	$150.8917	$150.89	$150.90	$150.90
Purchase #6	$179.53	9.666%	$196.8834	$196.88	$196.90	$196.90
Purchase #7	$205.49	9.573%	$225.1616	$225.16	$225.15	$225.20
7 purchase totals =	$812.32		$878.2584	$878.25	$878.25	$878.30