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	$182.43	3.196%	$188.2605	$188.26	$188.25	$188.30
Purchase #2	$32.77	5.301%	$34.5071	$34.51	$34.50	$34.50
Purchase #3	$26.83	8.347%	$29.0695	$29.07	$29.05	$29.10
Purchase #4	$91.25	13.372%	$103.452	$103.45	$103.45	$103.50
Purchase #5	$25.64	6.550%	$27.3194	$27.32	$27.30	$27.30
Purchase #6	$213.37	12.673%	$240.4104	$240.41	$240.40	$240.40
Purchase #7	$57.64	7.767%	$62.1169	$62.12	$62.10	$62.10
7 purchase totals =	$629.93		$685.1358	$685.14	$685.05	$685.20