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	$159.70	8.396%	$173.1084	$173.11	$173.10	$173.10
Purchase #2	$99.98	3.516%	$103.4953	$103.50	$103.50	$103.50
Purchase #3	$109.51	5.798%	$115.8594	$115.86	$115.85	$115.90
Purchase #4	$83.25	9.762%	$91.3769	$91.38	$91.40	$91.40
Purchase #5	$171.82	6.672%	$183.2838	$183.28	$183.30	$183.30
Purchase #6	$109.31	4.582%	$114.3186	$114.32	$114.30	$114.30
Purchase #7	$65.34	10.164%	$71.9812	$71.98	$72.00	$72.00
7 purchase totals =	$798.91		$853.4236	$853.43	$853.45	$853.50