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	$236.79	8.805%	$257.6394	$257.64	$257.65	$257.60
Purchase #2	$244.51	6.743%	$260.9973	$261.00	$261.00	$261.00
Purchase #3	$37.81	12.276%	$42.4516	$42.45	$42.45	$42.50
Purchase #4	$122.88	6.824%	$131.2653	$131.27	$131.25	$131.30
Purchase #5	$124.50	4.515%	$130.1212	$130.12	$130.10	$130.10
Purchase #6	$21.30	3.172%	$21.9756	$21.98	$22.00	$22.00
Purchase #7	$109.72	12.646%	$123.5952	$123.60	$123.60	$123.60
7 purchase totals =	$897.51		$968.0456	$968.06	$968.05	$968.10