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	$102.93	3.478%	$106.5099	$106.51	$106.50	$106.50
Purchase #2	$12.25	4.711%	$12.8271	$12.83	$12.85	$12.80
Purchase #3	$22.32	7.787%	$24.0581	$24.06	$24.05	$24.10
Purchase #4	$177.76	10.660%	$196.7092	$196.71	$196.70	$196.70
Purchase #5	$87.88	13.503%	$99.7464	$99.75	$99.75	$99.70
Purchase #6	$101.72	10.762%	$112.6671	$112.67	$112.65	$112.70
Purchase #7	$115.73	10.557%	$127.9476	$127.95	$127.95	$127.90
7 purchase totals =	$620.59		$680.4654	$680.48	$680.45	$680.40