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	$84.51	5.726%	$89.349	$89.35	$89.35	$89.30
Purchase #2	$92.80	8.383%	$100.5794	$100.58	$100.60	$100.60
Purchase #3	$42.61	10.332%	$47.0125	$47.01	$47.00	$47.00
Purchase #4	$10.46	7.272%	$11.2207	$11.22	$11.20	$11.20
Purchase #5	$180.54	6.200%	$191.7335	$191.73	$191.75	$191.70
Purchase #6	$150.71	12.212%	$169.1147	$169.11	$169.10	$169.10
Purchase #7	$238.57	13.798%	$271.4879	$271.49	$271.50	$271.50
7 purchase totals =	$800.20		$880.4977	$880.49	$880.50	$880.40