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	$234.94	12.407%	$264.089	$264.09	$264.10	$264.10
Purchase #2	$134.51	6.531%	$143.2948	$143.29	$143.30	$143.30
Purchase #3	$12.46	7.869%	$13.4405	$13.44	$13.45	$13.40
Purchase #4	$174.77	8.780%	$190.1148	$190.11	$190.10	$190.10
Purchase #5	$97.75	8.184%	$105.7499	$105.75	$105.75	$105.70
Purchase #6	$51.76	6.374%	$55.0592	$55.06	$55.05	$55.10
Purchase #7	$80.94	11.819%	$90.5063	$90.51	$90.50	$90.50
7 purchase totals =	$787.13		$862.2545	$862.25	$862.25	$862.20