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	$48.78	12.699%	$54.9746	$54.97	$54.95	$55.00
Purchase #2	$32.88	6.678%	$35.0757	$35.08	$35.10	$35.10
Purchase #3	$88.61	10.670%	$98.0647	$98.06	$98.05	$98.10
Purchase #4	$158.27	4.497%	$165.3874	$165.39	$165.40	$165.40
Purchase #5	$218.59	5.687%	$231.0212	$231.02	$231.00	$231.00
Purchase #6	$108.26	6.665%	$115.4755	$115.48	$115.50	$115.50
Purchase #7	$92.76	8.783%	$100.9071	$100.91	$100.90	$100.90
7 purchase totals =	$748.15		$800.9062	$800.91	$800.90	$801.00