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	$17.83	13.275%	$20.1969	$20.20	$20.20	$20.20
Purchase #2	$129.94	11.581%	$144.9884	$144.99	$145.00	$145.00
Purchase #3	$39.51	8.836%	$43.0011	$43.00	$43.00	$43.00
Purchase #4	$206.26	4.466%	$215.4716	$215.47	$215.45	$215.50
Purchase #5	$215.65	6.404%	$229.4602	$229.46	$229.45	$229.50
Purchase #6	$41.80	8.868%	$45.5068	$45.51	$45.50	$45.50
Purchase #7	$115.41	13.394%	$130.868	$130.87	$130.85	$130.90
7 purchase totals =	$766.40		$829.4930	$829.50	$829.45	$829.60