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	$71.29	13.434%	$80.8671	$80.87	$80.85	$80.90
Purchase #2	$152.72	10.219%	$168.3265	$168.33	$168.35	$168.30
Purchase #3	$9.83	3.513%	$10.1753	$10.18	$10.20	$10.20
Purchase #4	$100.62	4.178%	$104.8239	$104.82	$104.80	$104.80
Purchase #5	$60.45	11.655%	$67.4954	$67.50	$67.50	$67.50
Purchase #6	$164.44	6.218%	$174.6649	$174.66	$174.65	$174.70
Purchase #7	$34.55	5.755%	$36.5384	$36.54	$36.55	$36.50
7 purchase totals =	$593.90		$642.8915	$642.90	$642.90	$642.90