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	$248.47	7.158%	$266.2555	$266.26	$266.25	$266.30
Purchase #2	$49.72	7.358%	$53.3784	$53.38	$53.40	$53.40
Purchase #3	$227.99	5.303%	$240.0803	$240.08	$240.10	$240.10
Purchase #4	$223.37	3.251%	$230.6318	$230.63	$230.65	$230.60
Purchase #5	$226.55	8.374%	$245.5213	$245.52	$245.50	$245.50
Purchase #6	$223.85	11.331%	$249.2144	$249.21	$249.20	$249.20
Purchase #7	$196.81	9.501%	$215.5089	$215.51	$215.50	$215.50
7 purchase totals =	$1,396.76		$1,500.5906	$1,500.59	$1,500.60	$1,500.60