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	$239.60	7.348%	$257.2058	$257.21	$257.20	$257.20
Purchase #2	$145.41	11.616%	$162.3008	$162.30	$162.30	$162.30
Purchase #3	$56.66	4.736%	$59.3434	$59.34	$59.35	$59.30
Purchase #4	$97.52	8.221%	$105.5371	$105.54	$105.55	$105.50
Purchase #5	$230.54	8.776%	$250.7722	$250.77	$250.75	$250.80
Purchase #6	$77.41	7.285%	$83.0493	$83.05	$83.05	$83.00
Purchase #7	$77.38	9.123%	$84.4394	$84.44	$84.45	$84.40
7 purchase totals =	$924.52		$1,002.6480	$1,002.65	$1,002.65	$1,002.50