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	$32.45	12.716%	$36.5763	$36.58	$36.60	$36.60
Purchase #2	$61.69	3.718%	$63.9836	$63.98	$64.00	$64.00
Purchase #3	$47.81	12.691%	$53.8776	$53.88	$53.90	$53.90
Purchase #4	$166.60	9.780%	$182.8935	$182.89	$182.90	$182.90
Purchase #5	$106.96	10.440%	$118.1266	$118.13	$118.15	$118.10
Purchase #6	$121.97	5.342%	$128.4856	$128.49	$128.50	$128.50
Purchase #7	$231.40	8.180%	$250.3285	$250.33	$250.35	$250.30
7 purchase totals =	$768.88		$834.2717	$834.28	$834.40	$834.30