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	$65.50	5.367%	$69.0154	$69.02	$69.00	$69.00
Purchase #2	$189.81	7.271%	$203.6111	$203.61	$203.60	$203.60
Purchase #3	$26.64	3.409%	$27.5482	$27.55	$27.55	$27.50
Purchase #4	$152.43	7.736%	$164.222	$164.22	$164.20	$164.20
Purchase #5	$54.33	9.443%	$59.4604	$59.46	$59.45	$59.50
Purchase #6	$17.59	8.221%	$19.0361	$19.04	$19.05	$19.00
Purchase #7	$95.30	5.383%	$100.43	$100.43	$100.45	$100.40
7 purchase totals =	$601.60		$643.3232	$643.33	$643.30	$643.20