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	$89.92	3.755%	$93.2965	$93.30	$93.30	$93.30
Purchase #2	$215.92	10.658%	$238.9328	$238.93	$238.95	$238.90
Purchase #3	$27.73	4.780%	$29.0555	$29.06	$29.05	$29.10
Purchase #4	$149.38	6.170%	$158.5967	$158.60	$158.60	$158.60
Purchase #5	$98.90	11.108%	$109.8858	$109.89	$109.90	$109.90
Purchase #6	$205.72	6.410%	$218.9067	$218.91	$218.90	$218.90
Purchase #7	$115.99	8.845%	$126.2493	$126.25	$126.25	$126.20
7 purchase totals =	$903.56		$974.9233	$974.94	$974.95	$974.90