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	$86.68	3.268%	$89.5127	$89.51	$89.50	$89.50
Purchase #2	$179.53	4.214%	$187.0954	$187.10	$187.10	$187.10
Purchase #3	$114.32	3.217%	$117.9977	$118.00	$118.00	$118.00
Purchase #4	$85.58	11.535%	$95.4517	$95.45	$95.45	$95.50
Purchase #5	$139.54	4.430%	$145.7216	$145.72	$145.70	$145.70
Purchase #6	$85.56	7.301%	$91.8067	$91.81	$91.80	$91.80
Purchase #7	$148.47	4.803%	$155.601	$155.60	$155.60	$155.60
7 purchase totals =	$839.68		$883.1868	$883.19	$883.15	$883.20