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	$39.59	9.272%	$43.2608	$43.26	$43.25	$43.30
Purchase #2	$110.60	9.168%	$120.7398	$120.74	$120.75	$120.70
Purchase #3	$80.55	10.687%	$89.1584	$89.16	$89.15	$89.20
Purchase #4	$128.83	11.387%	$143.4999	$143.50	$143.50	$143.50
Purchase #5	$28.54	3.400%	$29.5104	$29.51	$29.50	$29.50
Purchase #6	$225.75	5.458%	$238.0714	$238.07	$238.05	$238.10
Purchase #7	$122.71	4.268%	$127.9473	$127.95	$127.95	$127.90
7 purchase totals =	$736.57		$792.1880	$792.19	$792.15	$792.20