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	$19.89	5.696%	$21.0229	$21.02	$21.00	$21.00
Purchase #2	$26.54	11.866%	$29.6892	$29.69	$29.70	$29.70
Purchase #3	$50.76	6.418%	$54.0178	$54.02	$54.00	$54.00
Purchase #4	$48.66	13.542%	$55.2495	$55.25	$55.25	$55.20
Purchase #5	$55.59	13.437%	$63.0596	$63.06	$63.05	$63.10
Purchase #6	$78.94	13.381%	$89.503	$89.50	$89.50	$89.50
Purchase #7	$107.42	10.129%	$118.3006	$118.30	$118.30	$118.30
7 purchase totals =	$387.80		$430.8426	$430.84	$430.80	$430.80