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	$242.98	6.723%	$259.3155	$259.32	$259.30	$259.30
Purchase #2	$59.47	5.580%	$62.7884	$62.79	$62.80	$62.80
Purchase #3	$172.33	11.712%	$192.5133	$192.51	$192.50	$192.50
Purchase #4	$161.98	3.805%	$168.1433	$168.14	$168.15	$168.10
Purchase #5	$237.91	11.126%	$264.3799	$264.38	$264.40	$264.40
Purchase #6	$214.35	13.307%	$242.8736	$242.87	$242.85	$242.90
Purchase #7	$132.56	11.677%	$148.039	$148.04	$148.05	$148.00
7 purchase totals =	$1,221.58		$1,338.0530	$1,338.05	$1,338.05	$1,338.00