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	$126.25	9.310%	$138.0039	$138.00	$138.00	$138.00
Purchase #2	$174.50	13.541%	$198.129	$198.13	$198.15	$198.10
Purchase #3	$169.39	7.561%	$182.1976	$182.20	$182.20	$182.20
Purchase #4	$129.36	12.729%	$145.8262	$145.83	$145.85	$145.80
Purchase #5	$69.89	12.482%	$78.6137	$78.61	$78.60	$78.60
Purchase #6	$54.66	5.385%	$57.6034	$57.60	$57.60	$57.60
Purchase #7	$27.83	9.636%	$30.5117	$30.51	$30.50	$30.50
7 purchase totals =	$751.88		$830.8855	$830.88	$830.90	$830.80