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	$30.55	9.687%	$33.5094	$33.51	$33.50	$33.50
Purchase #2	$91.52	9.239%	$99.9755	$99.98	$100.00	$100.00
Purchase #3	$206.80	4.849%	$216.8277	$216.83	$216.85	$216.80
Purchase #4	$124.62	3.611%	$129.12	$129.12	$129.10	$129.10
Purchase #5	$61.71	8.757%	$67.1139	$67.11	$67.10	$67.10
Purchase #6	$126.81	13.164%	$143.5033	$143.50	$143.50	$143.50
Purchase #7	$117.99	8.355%	$127.8481	$127.85	$127.85	$127.80
7 purchase totals =	$760.00		$817.8979	$817.90	$817.90	$817.80