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	$17.58	10.365%	$19.4022	$19.40	$19.40	$19.40
Purchase #2	$97.85	3.589%	$101.3618	$101.36	$101.35	$101.40
Purchase #3	$181.94	4.683%	$190.4603	$190.46	$190.45	$190.50
Purchase #4	$164.95	4.190%	$171.8614	$171.86	$171.85	$171.90
Purchase #5	$51.90	13.424%	$58.8671	$58.87	$58.85	$58.90
Purchase #6	$69.47	12.645%	$78.2545	$78.25	$78.25	$78.30
Purchase #7	$63.95	5.222%	$67.2895	$67.29	$67.30	$67.30
7 purchase totals =	$647.64		$687.4968	$687.49	$687.45	$687.70