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	$89.64	10.857%	$99.3722	$99.37	$99.35	$99.40
Purchase #2	$27.55	13.379%	$31.2359	$31.24	$31.25	$31.20
Purchase #3	$73.81	8.560%	$80.1281	$80.13	$80.15	$80.10
Purchase #4	$10.44	3.310%	$10.7856	$10.79	$10.80	$10.80
Purchase #5	$35.64	11.138%	$39.6096	$39.61	$39.60	$39.60
Purchase #6	$94.38	5.621%	$99.6851	$99.69	$99.70	$99.70
Purchase #7	$22.31	11.780%	$24.9381	$24.94	$24.95	$24.90
7 purchase totals =	$353.77		$385.7546	$385.77	$385.80	$385.70