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	$118.51	4.112%	$123.3831	$123.38	$123.40	$123.40
Purchase #2	$53.64	3.339%	$55.431	$55.43	$55.45	$55.40
Purchase #3	$246.72	11.624%	$275.3987	$275.40	$275.40	$275.40
Purchase #4	$47.56	9.348%	$52.0059	$52.01	$52.00	$52.00
Purchase #5	$74.67	11.296%	$83.1047	$83.10	$83.10	$83.10
Purchase #6	$43.33	13.189%	$49.0448	$49.04	$49.05	$49.00
Purchase #7	$124.39	8.436%	$134.8835	$134.88	$134.90	$134.90
7 purchase totals =	$708.82		$773.2517	$773.24	$773.30	$773.20