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	$172.94	8.817%	$188.1881	$188.19	$188.20	$188.20
Purchase #2	$103.31	5.311%	$108.7968	$108.80	$108.80	$108.80
Purchase #3	$61.35	7.776%	$66.1206	$66.12	$66.10	$66.10
Purchase #4	$177.54	8.311%	$192.2953	$192.30	$192.30	$192.30
Purchase #5	$233.82	8.426%	$253.5217	$253.52	$253.50	$253.50
Purchase #6	$225.30	9.656%	$247.055	$247.06	$247.05	$247.10
Purchase #7	$86.52	3.492%	$89.5413	$89.54	$89.55	$89.50
7 purchase totals =	$1,060.78		$1,145.5188	$1,145.53	$1,145.50	$1,145.50