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	$79.68	3.554%	$82.5118	$82.51	$82.50	$82.50
Purchase #2	$126.53	10.582%	$139.9194	$139.92	$139.90	$139.90
Purchase #3	$145.41	11.250%	$161.7686	$161.77	$161.75	$161.80
Purchase #4	$80.97	5.501%	$85.4242	$85.42	$85.40	$85.40
Purchase #5	$78.65	9.326%	$85.9849	$85.98	$86.00	$86.00
Purchase #6	$45.26	5.315%	$47.6656	$47.67	$47.65	$47.70
Purchase #7	$200.76	7.162%	$215.1384	$215.14	$215.15	$215.10
7 purchase totals =	$757.26		$818.4129	$818.41	$818.35	$818.40