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	$61.65	8.839%	$67.0992	$67.10	$67.10	$67.10
Purchase #2	$249.49	12.171%	$279.8554	$279.86	$279.85	$279.90
Purchase #3	$46.52	10.286%	$51.305	$51.31	$51.30	$51.30
Purchase #4	$103.52	5.785%	$109.5086	$109.51	$109.50	$109.50
Purchase #5	$167.37	12.472%	$188.2444	$188.24	$188.25	$188.20
Purchase #6	$150.84	9.626%	$165.3599	$165.36	$165.35	$165.40
Purchase #7	$25.87	11.597%	$28.8701	$28.87	$28.85	$28.90
7 purchase totals =	$805.26		$890.2426	$890.25	$890.20	$890.30