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	$68.85	13.611%	$78.2212	$78.22	$78.20	$78.20
Purchase #2	$100.63	3.367%	$104.0182	$104.02	$104.00	$104.00
Purchase #3	$168.58	3.844%	$175.0602	$175.06	$175.05	$175.10
Purchase #4	$58.63	5.370%	$61.7784	$61.78	$61.80	$61.80
Purchase #5	$65.86	6.123%	$69.8926	$69.89	$69.90	$69.90
Purchase #6	$203.68	13.400%	$230.9731	$230.97	$230.95	$231.00
Purchase #7	$47.49	13.358%	$53.8337	$53.83	$53.85	$53.80
7 purchase totals =	$713.72		$773.7774	$773.77	$773.75	$773.80