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	$162.63	11.553%	$181.4186	$181.42	$181.40	$181.40
Purchase #2	$153.34	13.830%	$174.5469	$174.55	$174.55	$174.50
Purchase #3	$47.45	8.365%	$51.4192	$51.42	$51.40	$51.40
Purchase #4	$235.84	12.372%	$265.0181	$265.02	$265.00	$265.00
Purchase #5	$80.35	6.843%	$85.8484	$85.85	$85.85	$85.80
Purchase #6	$100.30	4.267%	$104.5798	$104.58	$104.60	$104.60
Purchase #7	$110.59	12.172%	$124.051	$124.05	$124.05	$124.10
7 purchase totals =	$890.50		$986.8820	$986.89	$986.85	$986.80