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	$82.90	10.176%	$91.3359	$91.34	$91.35	$91.30
Purchase #2	$177.94	9.120%	$194.1681	$194.17	$194.15	$194.20
Purchase #3	$143.29	13.298%	$162.3447	$162.34	$162.35	$162.30
Purchase #4	$233.84	5.137%	$245.8524	$245.85	$245.85	$245.90
Purchase #5	$6.42	8.676%	$6.977	$6.98	$7.00	$7.00
Purchase #6	$5.25	10.640%	$5.8086	$5.81	$5.80	$5.80
Purchase #7	$85.83	4.297%	$89.5181	$89.52	$89.50	$89.50
7 purchase totals =	$735.47		$796.0048	$796.01	$796.00	$796.00