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	$6.58	12.317%	$7.3905	$7.39	$7.40	$7.40
Purchase #2	$155.52	5.840%	$164.6024	$164.60	$164.60	$164.60
Purchase #3	$24.55	11.239%	$27.3092	$27.31	$27.30	$27.30
Purchase #4	$67.55	13.734%	$76.8273	$76.83	$76.85	$76.80
Purchase #5	$123.63	11.729%	$138.1306	$138.13	$138.15	$138.10
Purchase #6	$72.54	7.442%	$77.9384	$77.94	$77.95	$77.90
Purchase #7	$11.52	8.346%	$12.4815	$12.48	$12.50	$12.50
7 purchase totals =	$461.89		$504.6799	$504.68	$504.75	$504.60