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	$207.50	4.344%	$216.5138	$216.51	$216.50	$216.50
Purchase #2	$88.69	13.260%	$100.4503	$100.45	$100.45	$100.50
Purchase #3	$87.32	4.169%	$90.9604	$90.96	$90.95	$91.00
Purchase #4	$113.83	5.444%	$120.0269	$120.03	$120.05	$120.00
Purchase #5	$138.29	9.872%	$151.942	$151.94	$151.95	$151.90
Purchase #6	$126.51	5.706%	$133.7287	$133.73	$133.75	$133.70
Purchase #7	$58.45	12.201%	$65.5815	$65.58	$65.60	$65.60
7 purchase totals =	$820.59		$879.2036	$879.20	$879.25	$879.20