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	$64.57	10.414%	$71.2943	$71.29	$71.30	$71.30
Purchase #2	$90.76	13.648%	$103.1469	$103.15	$103.15	$103.10
Purchase #3	$22.49	4.806%	$23.5709	$23.57	$23.55	$23.60
Purchase #4	$81.98	4.132%	$85.3674	$85.37	$85.35	$85.40
Purchase #5	$158.57	10.258%	$174.8361	$174.84	$174.85	$174.80
Purchase #6	$239.99	8.286%	$259.8756	$259.88	$259.90	$259.90
Purchase #7	$86.60	5.233%	$91.1318	$91.13	$91.15	$91.10
7 purchase totals =	$744.96		$809.2230	$809.23	$809.25	$809.20