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	$17.43	7.161%	$18.6782	$18.68	$18.70	$18.70
Purchase #2	$78.56	7.329%	$84.3177	$84.32	$84.30	$84.30
Purchase #3	$129.88	12.211%	$145.7396	$145.74	$145.75	$145.70
Purchase #4	$61.50	9.500%	$67.3425	$67.34	$67.35	$67.30
Purchase #5	$206.67	5.238%	$217.4954	$217.50	$217.50	$217.50
Purchase #6	$122.98	4.746%	$128.8166	$128.82	$128.80	$128.80
Purchase #7	$89.43	12.399%	$100.5184	$100.52	$100.50	$100.50
7 purchase totals =	$706.45		$762.9084	$762.92	$762.90	$762.80