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	$138.46	8.458%	$150.1709	$150.17	$150.15	$150.20
Purchase #2	$56.27	3.850%	$58.4364	$58.44	$58.45	$58.40
Purchase #3	$80.80	5.782%	$85.4719	$85.47	$85.45	$85.50
Purchase #4	$80.54	10.736%	$89.1868	$89.19	$89.20	$89.20
Purchase #5	$12.28	9.665%	$13.4669	$13.47	$13.45	$13.50
Purchase #6	$106.97	5.608%	$112.9689	$112.97	$112.95	$113.00
Purchase #7	$57.64	6.729%	$61.5186	$61.52	$61.50	$61.50
7 purchase totals =	$532.96		$571.2204	$571.23	$571.15	$571.30