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	$39.49	8.379%	$42.7989	$42.80	$42.80	$42.80
Purchase #2	$107.50	6.129%	$114.0887	$114.09	$114.10	$114.10
Purchase #3	$207.76	4.395%	$216.8911	$216.89	$216.90	$216.90
Purchase #4	$235.74	5.823%	$249.4671	$249.47	$249.45	$249.50
Purchase #5	$74.55	4.607%	$77.9845	$77.98	$78.00	$78.00
Purchase #6	$189.69	11.858%	$212.1834	$212.18	$212.20	$212.20
Purchase #7	$80.47	12.369%	$90.4233	$90.42	$90.40	$90.40
7 purchase totals =	$935.20		$1,003.8370	$1,003.83	$1,003.85	$1,003.90