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	$28.94	12.638%	$32.5974	$32.60	$32.60	$32.60
Purchase #2	$27.25	7.652%	$29.3352	$29.34	$29.35	$29.30
Purchase #3	$90.96	9.198%	$99.3265	$99.33	$99.35	$99.30
Purchase #4	$91.69	6.577%	$97.7205	$97.72	$97.70	$97.70
Purchase #5	$219.41	4.190%	$228.6033	$228.60	$228.60	$228.60
Purchase #6	$40.64	7.751%	$43.79	$43.79	$43.80	$43.80
Purchase #7	$94.81	6.182%	$100.6712	$100.67	$100.65	$100.70
7 purchase totals =	$593.70		$632.0441	$632.05	$632.05	$632.00