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	$56.25	5.785%	$59.5041	$59.50	$59.50	$59.50
Purchase #2	$183.53	4.537%	$191.8568	$191.86	$191.85	$191.90
Purchase #3	$52.92	10.341%	$58.3925	$58.39	$58.40	$58.40
Purchase #4	$214.38	7.366%	$230.1712	$230.17	$230.15	$230.20
Purchase #5	$61.60	9.806%	$67.6405	$67.64	$67.65	$67.60
Purchase #6	$42.56	11.214%	$47.3327	$47.33	$47.35	$47.30
Purchase #7	$166.47	5.328%	$175.3395	$175.34	$175.35	$175.30
7 purchase totals =	$777.71		$830.2373	$830.23	$830.25	$830.20