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	$72.52	11.812%	$81.0861	$81.09	$81.10	$81.10
Purchase #2	$103.67	12.133%	$116.2483	$116.25	$116.25	$116.20
Purchase #3	$80.49	11.729%	$89.9307	$89.93	$89.95	$89.90
Purchase #4	$103.90	9.335%	$113.5991	$113.60	$113.60	$113.60
Purchase #5	$246.58	9.631%	$270.3281	$270.33	$270.35	$270.30
Purchase #6	$224.41	10.430%	$247.816	$247.82	$247.80	$247.80
Purchase #7	$13.89	6.473%	$14.7891	$14.79	$14.80	$14.80
7 purchase totals =	$845.46		$933.7974	$933.81	$933.85	$933.70