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	$71.36	10.244%	$78.6701	$78.67	$78.65	$78.70
Purchase #2	$235.51	8.691%	$255.9782	$255.98	$256.00	$256.00
Purchase #3	$59.91	6.522%	$63.8173	$63.82	$63.80	$63.80
Purchase #4	$157.86	13.690%	$179.471	$179.47	$179.45	$179.50
Purchase #5	$35.57	13.339%	$40.3147	$40.31	$40.30	$40.30
Purchase #6	$180.51	3.435%	$186.7105	$186.71	$186.70	$186.70
Purchase #7	$61.88	11.461%	$68.9721	$68.97	$68.95	$69.00
7 purchase totals =	$802.60		$873.9339	$873.93	$873.85	$874.00