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	$29.72	12.317%	$33.3806	$33.38	$33.40	$33.40
Purchase #2	$75.78	8.287%	$82.0599	$82.06	$82.05	$82.10
Purchase #3	$50.26	13.694%	$57.1426	$57.14	$57.15	$57.10
Purchase #4	$167.75	12.429%	$188.5996	$188.60	$188.60	$188.60
Purchase #5	$195.59	11.499%	$218.0809	$218.08	$218.10	$218.10
Purchase #6	$104.26	9.643%	$114.3138	$114.31	$114.30	$114.30
Purchase #7	$86.51	3.524%	$89.5586	$89.56	$89.55	$89.60
7 purchase totals =	$709.87		$783.1360	$783.13	$783.15	$783.20