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	$132.98	4.864%	$139.4481	$139.45	$139.45	$139.40
Purchase #2	$148.83	11.275%	$165.6106	$165.61	$165.60	$165.60
Purchase #3	$89.49	13.441%	$101.5184	$101.52	$101.50	$101.50
Purchase #4	$113.34	4.323%	$118.2397	$118.24	$118.25	$118.20
Purchase #5	$101.43	7.400%	$108.9358	$108.94	$108.95	$108.90
Purchase #6	$181.59	9.745%	$199.2859	$199.29	$199.30	$199.30
Purchase #7	$108.38	4.149%	$112.8767	$112.88	$112.90	$112.90
7 purchase totals =	$876.04		$945.9152	$945.93	$945.95	$945.80