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	$233.67	9.149%	$255.0485	$255.05	$255.05	$255.00
Purchase #2	$169.27	11.752%	$189.1626	$189.16	$189.15	$189.20
Purchase #3	$31.69	12.158%	$35.5429	$35.54	$35.55	$35.50
Purchase #4	$101.86	3.158%	$105.0767	$105.08	$105.10	$105.10
Purchase #5	$6.92	4.738%	$7.2479	$7.25	$7.25	$7.20
Purchase #6	$52.25	13.769%	$59.4443	$59.44	$59.45	$59.40
Purchase #7	$186.96	5.144%	$196.5772	$196.58	$196.60	$196.60
7 purchase totals =	$782.62		$848.1001	$848.10	$848.15	$848.00