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	$43.33	10.450%	$47.858	$47.86	$47.85	$47.90
Purchase #2	$160.94	10.213%	$177.3768	$177.38	$177.40	$177.40
Purchase #3	$106.90	4.347%	$111.5469	$111.55	$111.55	$111.50
Purchase #4	$72.72	8.386%	$78.8183	$78.82	$78.80	$78.80
Purchase #5	$148.30	9.634%	$162.5872	$162.59	$162.60	$162.60
Purchase #6	$239.25	4.359%	$249.6789	$249.68	$249.70	$249.70
Purchase #7	$77.80	9.531%	$85.2151	$85.22	$85.20	$85.20
7 purchase totals =	$849.24		$913.0812	$913.10	$913.10	$913.10