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	$40.79	12.440%	$45.8643	$45.86	$45.85	$45.90
Purchase #2	$102.53	8.716%	$111.4665	$111.47	$111.45	$111.50
Purchase #3	$74.41	13.360%	$84.3512	$84.35	$84.35	$84.40
Purchase #4	$12.85	12.304%	$14.4311	$14.43	$14.45	$14.40
Purchase #5	$99.98	13.199%	$113.1764	$113.18	$113.20	$113.20
Purchase #6	$228.72	11.416%	$254.8307	$254.83	$254.85	$254.80
Purchase #7	$16.98	11.565%	$18.9437	$18.94	$18.95	$18.90
7 purchase totals =	$576.26		$643.0639	$643.06	$643.10	$643.10