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	$7.30	9.745%	$8.0114	$8.01	$8.00	$8.00
Purchase #2	$111.55	6.811%	$119.1477	$119.15	$119.15	$119.10
Purchase #3	$78.92	6.363%	$83.9417	$83.94	$83.95	$83.90
Purchase #4	$79.27	11.174%	$88.1276	$88.13	$88.15	$88.10
Purchase #5	$76.84	9.150%	$83.8709	$83.87	$83.85	$83.90
Purchase #6	$77.68	5.763%	$82.1567	$82.16	$82.15	$82.20
Purchase #7	$37.88	7.384%	$40.6771	$40.68	$40.70	$40.70
7 purchase totals =	$469.44		$505.9331	$505.94	$505.95	$505.90