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	$9.89	10.410%	$10.9195	$10.92	$10.90	$10.90
Purchase #2	$248.61	13.559%	$282.319	$282.32	$282.30	$282.30
Purchase #3	$118.50	7.229%	$127.0664	$127.07	$127.05	$127.10
Purchase #4	$241.71	9.518%	$264.716	$264.72	$264.70	$264.70
Purchase #5	$99.32	6.623%	$105.898	$105.90	$105.90	$105.90
Purchase #6	$137.87	10.134%	$151.8417	$151.84	$151.85	$151.80
Purchase #7	$130.38	6.844%	$139.3032	$139.30	$139.30	$139.30
7 purchase totals =	$986.28		$1,082.0638	$1,082.07	$1,082.00	$1,082.00