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	$43.53	4.531%	$45.5023	$45.50	$45.50	$45.50
Purchase #2	$45.40	8.185%	$49.116	$49.12	$49.10	$49.10
Purchase #3	$56.98	3.835%	$59.1652	$59.17	$59.15	$59.20
Purchase #4	$148.86	10.478%	$164.4576	$164.46	$164.45	$164.50
Purchase #5	$36.77	13.845%	$41.8608	$41.86	$41.85	$41.90
Purchase #6	$48.37	3.385%	$50.0073	$50.01	$50.00	$50.00
Purchase #7	$161.92	12.490%	$182.1438	$182.14	$182.15	$182.10
7 purchase totals =	$541.83		$592.2530	$592.26	$592.20	$592.30