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	$99.98	3.336%	$103.3153	$103.32	$103.30	$103.30
Purchase #2	$94.59	4.239%	$98.5997	$98.60	$98.60	$98.60
Purchase #3	$81.34	5.497%	$85.8113	$85.81	$85.80	$85.80
Purchase #4	$150.64	7.653%	$162.1685	$162.17	$162.15	$162.20
Purchase #5	$137.77	3.664%	$142.8179	$142.82	$142.80	$142.80
Purchase #6	$16.50	13.448%	$18.7189	$18.72	$18.70	$18.70
Purchase #7	$220.67	9.466%	$241.5586	$241.56	$241.55	$241.60
7 purchase totals =	$801.49		$852.9902	$853.00	$852.90	$853.00