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	$37.35	13.522%	$42.4005	$42.40	$42.40	$42.40
Purchase #2	$124.80	6.801%	$133.2876	$133.29	$133.30	$133.30
Purchase #3	$122.88	9.245%	$134.2403	$134.24	$134.25	$134.20
Purchase #4	$114.58	7.240%	$122.8756	$122.88	$122.90	$122.90
Purchase #5	$190.54	3.256%	$196.744	$196.74	$196.75	$196.70
Purchase #6	$20.41	3.671%	$21.1593	$21.16	$21.15	$21.20
Purchase #7	$39.38	11.536%	$43.9229	$43.92	$43.90	$43.90
7 purchase totals =	$649.94		$694.6302	$694.63	$694.65	$694.60