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	$18.63	10.818%	$20.6454	$20.65	$20.65	$20.60
Purchase #2	$52.84	5.281%	$55.6305	$55.63	$55.65	$55.60
Purchase #3	$247.47	3.794%	$256.859	$256.86	$256.85	$256.90
Purchase #4	$216.54	11.252%	$240.9051	$240.91	$240.90	$240.90
Purchase #5	$121.30	4.709%	$127.012	$127.01	$127.00	$127.00
Purchase #6	$40.85	5.397%	$43.0547	$43.05	$43.05	$43.10
Purchase #7	$83.49	3.721%	$86.5967	$86.60	$86.60	$86.60
7 purchase totals =	$781.12		$830.7034	$830.71	$830.70	$830.70