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	$221.88	12.703%	$250.0654	$250.07	$250.05	$250.10
Purchase #2	$68.25	5.759%	$72.1805	$72.18	$72.20	$72.20
Purchase #3	$157.59	13.452%	$178.789	$178.79	$178.80	$178.80
Purchase #4	$229.97	4.334%	$239.9369	$239.94	$239.95	$239.90
Purchase #5	$20.35	5.264%	$21.4212	$21.42	$21.40	$21.40
Purchase #6	$137.90	3.245%	$142.3749	$142.37	$142.35	$142.40
Purchase #7	$79.69	12.793%	$89.8847	$89.88	$89.90	$89.90
7 purchase totals =	$915.63		$994.6526	$994.65	$994.65	$994.70