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	$230.74	5.574%	$243.6014	$243.60	$243.60	$243.60
Purchase #2	$90.35	10.630%	$99.9542	$99.95	$99.95	$100.00
Purchase #3	$169.54	5.315%	$178.5511	$178.55	$178.55	$178.60
Purchase #4	$91.30	8.867%	$99.3956	$99.40	$99.40	$99.40
Purchase #5	$228.60	3.457%	$236.5027	$236.50	$236.50	$236.50
Purchase #6	$228.64	6.195%	$242.8042	$242.80	$242.80	$242.80
Purchase #7	$140.47	5.699%	$148.4754	$148.48	$148.50	$148.50
7 purchase totals =	$1,179.64		$1,249.2846	$1,249.28	$1,249.30	$1,249.40