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	$98.68	9.638%	$108.1908	$108.19	$108.20	$108.20
Purchase #2	$178.87	6.395%	$190.3087	$190.31	$190.30	$190.30
Purchase #3	$123.60	5.571%	$130.4858	$130.49	$130.50	$130.50
Purchase #4	$53.95	11.117%	$59.9476	$59.95	$59.95	$59.90
Purchase #5	$223.76	11.705%	$249.9511	$249.95	$249.95	$250.00
Purchase #6	$169.70	8.573%	$184.2484	$184.25	$184.25	$184.20
Purchase #7	$174.27	6.647%	$185.8537	$185.85	$185.85	$185.90
7 purchase totals =	$1,022.83		$1,108.9861	$1,108.99	$1,109.00	$1,109.00