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	$90.70	13.759%	$103.1794	$103.18	$103.20	$103.20
Purchase #2	$238.70	12.868%	$269.4159	$269.42	$269.40	$269.40
Purchase #3	$95.96	9.442%	$105.0205	$105.02	$105.00	$105.00
Purchase #4	$238.39	9.733%	$261.5925	$261.59	$261.60	$261.60
Purchase #5	$88.74	12.169%	$99.5388	$99.54	$99.55	$99.50
Purchase #6	$100.80	4.230%	$105.0638	$105.06	$105.05	$105.10
Purchase #7	$180.79	3.718%	$187.5118	$187.51	$187.50	$187.50
7 purchase totals =	$1,034.08		$1,131.3227	$1,131.32	$1,131.30	$1,131.30