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	$190.41	7.360%	$204.4242	$204.42	$204.40	$204.40
Purchase #2	$129.91	7.135%	$139.1791	$139.18	$139.20	$139.20
Purchase #3	$169.83	10.720%	$188.0358	$188.04	$188.05	$188.00
Purchase #4	$18.81	5.416%	$19.8287	$19.83	$19.85	$19.80
Purchase #5	$172.75	3.281%	$178.4179	$178.42	$178.40	$178.40
Purchase #6	$85.81	4.237%	$89.4458	$89.45	$89.45	$89.40
Purchase #7	$147.49	11.270%	$164.1121	$164.11	$164.10	$164.10
7 purchase totals =	$915.01		$983.4436	$983.45	$983.45	$983.30