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	$115.47	10.643%	$127.7595	$127.76	$127.75	$127.80
Purchase #2	$230.60	13.535%	$261.8117	$261.81	$261.80	$261.80
Purchase #3	$38.34	4.645%	$40.1209	$40.12	$40.10	$40.10
Purchase #4	$80.48	10.741%	$89.1244	$89.12	$89.10	$89.10
Purchase #5	$116.78	5.208%	$122.8619	$122.86	$122.85	$122.90
Purchase #6	$37.88	4.330%	$39.5202	$39.52	$39.50	$39.50
Purchase #7	$162.40	13.188%	$183.8173	$183.82	$183.80	$183.80
7 purchase totals =	$781.95		$865.0159	$865.01	$864.90	$865.00