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	$248.88	11.167%	$276.6724	$276.67	$276.65	$276.70
Purchase #2	$156.46	7.349%	$167.9582	$167.96	$167.95	$168.00
Purchase #3	$16.37	8.495%	$17.7606	$17.76	$17.75	$17.80
Purchase #4	$93.74	10.256%	$103.354	$103.35	$103.35	$103.40
Purchase #5	$35.65	12.619%	$40.1487	$40.15	$40.15	$40.10
Purchase #6	$111.74	13.697%	$127.045	$127.05	$127.05	$127.00
Purchase #7	$7.51	5.764%	$7.9429	$7.94	$7.95	$7.90
7 purchase totals =	$670.35		$740.8818	$740.88	$740.85	$740.90