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	$136.27	4.386%	$142.2468	$142.25	$142.25	$142.20
Purchase #2	$80.86	5.656%	$85.4334	$85.43	$85.45	$85.40
Purchase #3	$48.50	13.621%	$55.1062	$55.11	$55.10	$55.10
Purchase #4	$122.79	13.865%	$139.8148	$139.81	$139.80	$139.80
Purchase #5	$82.64	13.410%	$93.722	$93.72	$93.70	$93.70
Purchase #6	$28.59	3.803%	$29.6773	$29.68	$29.70	$29.70
Purchase #7	$43.43	10.754%	$48.1005	$48.10	$48.10	$48.10
7 purchase totals =	$543.08		$594.1010	$594.10	$594.10	$594.00