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	$142.72	5.683%	$150.8308	$150.83	$150.85	$150.80
Purchase #2	$107.94	7.606%	$116.1499	$116.15	$116.15	$116.10
Purchase #3	$170.37	8.197%	$184.3352	$184.34	$184.35	$184.30
Purchase #4	$82.33	10.234%	$90.7557	$90.76	$90.75	$90.80
Purchase #5	$73.48	4.840%	$77.0364	$77.04	$77.05	$77.00
Purchase #6	$94.48	8.401%	$102.4173	$102.42	$102.40	$102.40
Purchase #7	$43.67	3.512%	$45.2037	$45.20	$45.20	$45.20
7 purchase totals =	$714.99		$766.7290	$766.74	$766.75	$766.60